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Frequently asked questions about e-mail and mail settings

Tip: Is your email question not listed here? Then email us so we can add it.

Apple Mail does not work

When you use Apple devices for email, you may find that your IP address gets blocked by the servers firewall. The cause lies in the fact that Apple sometimes uses port 585 which is rather unusual.

Since the security software monitors the use of unusual ports, it will then probably intervene and block your IP address after a number of attempts.

For mail, use the ports recommended by your hosting provider.

Can I forward my e-mails to another address?

The short answer is yes...but...

It is fine if you do this from, say, to But as soon as you want to do this to another domain, this is not a good idea.

Learn more about forwarding email and why this requires extra attention.

Error message ‘550 the content of this message looked like spam’

Sometimes you get an error message  when sending mail. The error message '550 the content of this message looked like spam' indicates that the sent message cannot be delivered. In this article, we will explain why you are getting this error message and how to resolve it.

The reason you get this message is because the email cannot be delivered and the incoming server has a spam filter that classifies the email as SPAM. And this does not happen without reason.

At the incoming mail server, all e-mails are viewed and rated by the spam filter. Each mail gets points, the more points the more likely it is to be rated as spam. The points are awarded by a certain algorithm, it looks at, for example:

  • Is the sent mail server blacklisted?
  • Does the name of the mail server match the name of the sender?
  • Does the content of the e-mail contain potentially harmful content or does the attachment contain potentially malware?
  • Does the content of the e-mail contain certain words that indicate spam or links to blacklisted (phishing) sites?

The algorithm used is very precise and based on millions of other mails already processed.

If the point score of a message exceeds a certain threshold, the message is classified SPAM. To inform the sender, the sender receives the so-called 550 error message. The sender then knows that his mail could not be delivered.

If this happens to you, you should check your mail and a number of settings.

Check SMTP server settings

The SMTP server is the server that sends your mail, which you set up separately in your mail programme. The settings include the option "This server requires authentication" (or something similar). In many cases, the SMTP server also requires this so you have to tick it.

Check the content of your message

Check your e-mail message to make sure it does not contain any 'wrong' words or links to blacklisted sites.
If you send an attachment that may contain blacklisted text or links, and you cannot send it by e-mail  please use, for example, WeTransfer (or another service)  to send the attachment anyway.

Still an error message?

If you keep getting an error message and can't figure it out,  please contact whoever arranges the web hosting and include the original message headers of your mail. Based on this, a solution can be found.

How can I automatically archive messages in Outlook?

What exactly is archiving in Outlook and why should you do it?

With archiving e-mails, you move e-mails from your current mailbox to a local archive file. This can be useful, for example, to keep the amount of e-mail you have on the server below a certain limit. Depending on your settings in outlook, the amount of mail you leave on the server can quickly increase. When you use IMAP as your setting, you leave all mail on the server and use the mail programme to look into it. For speed, your programme does have a local shadow copy but this is not the same as the archive file or a local file you created yourself.

Where can I find the local archive file?

If you turn on the auto-archive option then the program will create a file in this location :
C:username>DocumentsOutlook files

If this file did not already exist, it will also be created the first time you click archive, for example, an individual email.


Right-click on the message you want to archive.

archiveer een enkel e-mailbericht

Or first create an archive folder using this option:

archiefmap aanmaken via accountgegevens

After you have done this, this message may appear :

archiefbestand aanmaken in outlook

Then click on "Create archive folder". The archive file will be created, the mail will be saved in it and disappear from your inbox.

Settings for Autoarchiving

If you want to change the default settings for archiving, go to "File > Options". In the window you will then see, click on "Advanced" in the left-hand part of the window and then on "Settings for AutoArchiving".

In the left-hand part of the window, click on "Advanced" and then on "Settings for AutoArchiving".

instellingen voor autoarchiveren

Here you will find options for frequency of archiving, whether to delete or archive items and in which folder.

You can, by the way, create multiple files to apply different settings.



How can I see which mails and folders in Thunderbird take up the most space?

Everyone who uses email will sometimes get the message that your mailbox is too full and that action needs to be taken. Of course, you can just drag and drop everything into a "offline folder" which you then save on your computer. Alternatively, you can be a little more selective and look for the mails and folders that take up the most space and work on those.

How much space does a folder of emails take up?

To get a quick and easy answer to this, take the following steps:

Turn on folder column display via "View > Design > Folder panel columns".


thunderbird folderruimte tonen in mappenkolom


You can now make some additional columns visible by clicking on the very small icon that appears at the top of your folder list :

thunderbird kolommen zichtaar maken


The names speak for themselves. If you have selected "Size" then sometimes you have to click on the folder to immediately see how much space it takes up.

If you have applied these settings you will see the number of emails in the folder and the amount of space they take up.


toont de thunderbird folderruimte en aantal mailtjes per account

How do I change my server settings in Outlook?

Changing your server settings is a little bit hidden so we have created a little guide for this.

To get to the right settings, first click on "File" or "File" if you have the English version.


Klik in outlook op bestand in het menu


Then select the account whose settings you want to change (1) and click the small arrow at the bottom of the button (2).

Selecteer in outlook het account waarvan je de instellingen wilt aanpassen


Then click on server settings.

klik op serverinstellingen


You will now see the options for the incoming server.

serverinstellingen wijzigen inkomende server


You can also view them for the outgoing server.

serverinstellingen wijzigen uitgaande server


Bear in mind that you may have different settings for different providers. If something is not working, send screenshots of the above settings together with your error message to your provider so that they can help you solve the problem. In almost all cases, it is a minor adjustment to your settings that causes it not to work. This is because the requirements for secure emailing are getting tighter.



How do I clean up emails in Outlook?

If you use e-mail via IMAP, deleted mails are not immediately removed from the server but are marked for deletion. So they are still on the server and taking up space there. Sometimes you just want to clear all emails from a folder, the option described below can be helpful for this.


When you want to delete mails permanently, there is an option to empty that folder:

outlook map leegmaken imap


Then just confirm and the emails are gone for good.

map leegmaken bevestiging

How do I create a local folder in Thunderbird?

Using an offline folder (a folder that resides only on your PC) can be useful for storing e-mail to free up more space on the server where the e-mail resides, for example.

You can create as many folders as you need.

Step 1


Click your right mouse button on "Local Folders" and choose "New Folder"


thunderbird offline folder aanmaken

Geef de folder een naam die je handig vindt.


Step 2

You can now easily drag and drop emails into this folder but you can also move or copy several emails at once.

To do this, select the mails you want to move or copy and then right-click on them.

Then select "Move to > Local Folder > e-mail backup" or the name you chose for your folder.


thunderbird verplaats berichten naar offline folder


Where do I find the local Thunderbird folder?

In Thunderbird, go to the local folder whose location you want to know and right-click on it :


thunderbird archief locatie


The field you then see contains the path to the folder you are looking for.

thunderbird archief locatie 2

Copy this and paste it into your explorer without the bit after "Local Folders"

thunderbird archief locatie 3

The files you see in that folder contain your mail files. It's a good idea to back them up regularly, preferably automatically.



How do I create an offline folder/folder in Outlook?

To store your data on a local PC, or other medium, you can use a local data file (PST).

You can create a local data file (PST).

You create it by choosing "New items > More items > Outlook data file" from the menu.


outlook gegevensbestand offline via het menu


Outlook will then ask where you want to save this file and what name you want to give it.

outlook gegevensbestand offline naam geven


Once you have done this, an additional item will appear in outlook which may look like this:

inbox folder


But if desired, create an additional folder so you can easily see what mail is in this file:

create new folder outlook


You can now save emails in here which will then no longer take up space online. Make sure you make a backup of this "just in case".

Mailing via Gmail SMTP in Joomla gives error message

When you want to mail in Joomla via Gmail/Google's SMTP, you may get a message "Could not authenticate".

office365 could not authenticate


There is a good chance that you have recently enabled two-step verification in Google.
Supposing you have checked all the settings for the mailing in Joomla via SMTP, the solution in this case is to create a so-called Application Password (App password) in Gmail.

Creating App password is explained in this instruction.

The password you obtain with this should be set in the smtp data in your Joomla site.

Always click the button at the bottom to send a test mail.


Mailing via SMTP in Joomla gives error "Could not authenticate" message for Office365

If you want to mail in Joomla via SMTP and you are using Microsoft 365 (Office 365) you may get a message "Could not authenticate".

office365 could not authenticate


As long as you've checked all the settings for the mail in Joomla via SMTP, you might want to take a look at the settings in Microsoft 365 because since April 2020, some important settings have changed for new accounts in Office365.

In your Joomla log file (you can find these files in: administrator/logs) you may see notifications similar to this:

mail Error in Mail API: SMTP INBOUND: "535 5.7.139 Authentication unsuccessful, the request did not meet the criteria to be authenticated successfully. Contact your administrator.

If you see nothing then you may still need to adjust your logging, these settings can be found in the General configuration on the logging tab.

Exchange Online / Microsoft 365 / Office365

If you are an administrator or want to get something modified in Office365, this article may be helpful :

So the bottom line is that a default setting has been changed causing you to get the above error message.

For fans, a nice discussion in the forum :

Another tip is to disable 2FA for SMTP if you use Office 365 to send your mail.


What data do I need to set up my mail properly?

To set up your mail properly, you must have the following information :

  • a user name and password
  • the server names for the outgoing (SMTP) server
  • the server names for the incoming (POP3 or IMAP) server
  • the incoming server port used (995 for POP3 and 993 for IMAP or 143 with STARTTLS)
  • the outgoing server port used (465 for SSL and 587 for STARTTLS - preferred)

If your mail programme sets a port as 25, 26 or 110 then you need to change it as those ports are from unsecured connections.

A number of settings from major mail providers listed for convenience.
This list may change over time so if you come across something that doesn't work (anymore) then please let us know so we can adjust it.


The email providerIMAPPOPSMTP
993 - SSL/TLS of 143 - STARTTLS
995 - SSL/TLS
465 - SSL/TLS
993 - SSL/TLS of 143 - STARTTLS
995 - SSL/TLS
465 - SSL/TLS
993 - SSL/TLS of 143 - STARTTLS
993 - SSL/TLS of 143 - STARTTLS
995 - SSL/TLS
Microsoft 365
Office 365
993 - SSL/TLS of 143 - STARTTLS
995 - SSL/TLS
993 - SSL/TLS of 143 - STARTTLS
995 - SSL/TLS
993 - SSL of 143 - STARTTLS
995 - SSL
465 of 587 - SSL of TLS/STARTTLS
What is a blacklist?

A blacklist (= blacklist) is a list of IP addresses or e-mail addresses/servers that send spam. This list is maintained on the mail server.
The mail coming from these servers is always considered spam and is not accepted.

This is in contrast to a whitelist. Mail coming from servers on a whitelist is accepted.

Does your hoster use a blacklist?

Probably yes, but check to be sure.

What is a whitelist?

A whitelist (= white list) is a list of IP addresses or e-mail addresses/servers that is consulted on the mail server whether the mail being sent is valid. Mail sent from servers on the whitelist is always accepted.

This is in contrast to a blacklist. Mail coming from servers that are blacklisted is not accepted.

Does your hoster use a whitelist?

Probably yes, but check to be sure.

What is greylisting?

Greylisting is an effective way to stop spam mail. Every mail that comes in to the mail server is checked and then determined whether the sender is trustworthy or not to make a trade-off whether to mark the mail as spam or not. Often mails with a correct SPF record and many major mail providers automatically whitelist.

If your hoster uses whitelisting and blacklisting then probably greylisting will also be active. To understand this concept properly, I will explain.

A mail sent from an outgoing mail server arrives at an incoming mail server. But before this actually happens, the outgoing mail server will introduce itself to the incoming mail server, a kind of 'handshake'. Also, the outgoing mail server will introduce itself and indicate that it has an e-mail, how big that mail message is, whether there is an attachment and who the sender (e-mail address) is.

The incoming mail server processes the data and decides what to do with the mail:

  • If the incoming mail server is blacklisted, the mail will be rejected.
  • If the incoming mail server is on the whitelist, that mail server is trusted and the mail will be further checked for spam characteristics. So this is often the case for large mail providers like Microsoft, Google, Apple etc.
  • Greylisting is in between. If the outgoing mail server is not on either list, it will be seen as an unknown server. The incoming mail server will now check if the sender of the mail matches the name of the mail server. If they do not match, the mail is temporarily placed on the greylist.

After that, the incoming mail server sends a message back to the outgoing mail server that the mail could not be delivered.

A healthy (and valid) mail server that gets this message will keep it and after some time (half an hour) make another attempt to see if the mail can be delivered then. This is standard in the entire mail protocol, also because a receiving mail server may be temporarily full, have a failure, or something similar.

A server that sends spam has no time and capacity at all to store those messages and mail them again later, it only wants one thing: to deliver as much mail as possible, one after the other. Keeping track of rejected mail will otherwise end up in a queue which will then fill up quickly, and a server set up to spam does not want that.

In this way, healthy and unhealthy mail servers are separated. The healthy mail server will (fully automatically) make a second attempt and then the incoming mail server will recognise it and let the mail in after all.


What is the difference between POP3 and IMAP?

Both POP3 (Post Office Protocol) and IMAP (Internet Message Access Protocol) are so-called protocols for getting email in.

It is common when bringing in e-mail with POP that you pick up the mails all from the server and store them on your PC. Once this is done, the e-mails are deleted from the server. Sometimes immediately but often after, say, 1 or 2 weeks.

Using POP3 is fine if you don't need to share mail with several people on different devices. One problem with using it may be that it only pulls in the "inbox" folder and not the spam folder. You may then start missing e-mails that ended up in the spam folder, rightly or wrongly. To see these, you would then have to log in to this mailbox using webmail to still be able to see them.

If you do want multiple people to read the mail, it may be more convenient to use the IMAP protocol where the mail remains on the server. That way, multiple people or devices can look at the same mail because it is not deleted from the server after reading it. This happens only when the mail is explicitly deleted from the server.

Another advantage is that you do get to see all folders like the spam folder or sometimes the junk folder.

When do I use SSL and when STARTTLS for email?

It is important for all e-mail you send to be sent securely. You can do this by using so-called encryption (also called encryption) while sending but also while receiving. This prevents email that is intercepted from being read by other parties.

You can either encrypt the content of the email or the sending of email. In this explanation, we are talking about encrypting the sending of email using the SSL or TLS transfer protocol. TLS (Transport Layer Security) is better known as SSL (Secure Socket Layer) which is the old name.

SSL, TLS and STARTTLS, what are the differences?

SSL is not new, it has been around since around 1994 with version 1.0 never appearing on the market and version 2.0 quickly being replaced by version 3.0 due to weaknesses in the cryptography. Meanwhile, since 2014, version 3.0 must also be considered insecure.

TLS has been developed since 1999 and has reached version 1.3 as of 2018. TLS is based on Secure Socket Layer (SSL). TLS is also more secure than SSL on many fronts and is therefore preferred.

What to look out for,

In any case, it is important that you prefer to use STARTTLS as your encryption method and do not send or receive your e-mail unsecured. Also make sure you use an up-to-date mail programme because if it is too old, it does not support recent versions of security. This can become a problem, sometimes causing your e-mail not to arrive or possibly to be returned.

A summary (not 100 per cent complete) for inspiration:


TLS versie1.
Office 365 As of October 2018, TSL 1.0 and TSL 1.1 are no longer supported.
Outlook 2003 There is no support for TLS, find a newer mail programme if you want to mail securely.
Gmail Gmail uses a recent version and updates it whenever possible.
Which Outlook folder contains the most mail?

If your mailbox is too full and you would like to know which folder contains the most email you can do this in the following way:

Right-click on the inbox of the account whose size you want to know.


klik met de rechter muisknop op de inbox en ga naar eigenschappen


Then click on the "folder size" button.

klik op button mapgrootte


You can now see which folder has the most emails so you can clean up in a targeted way.

mapgrootte folders

Don't forget to empty the recycle bin after deleting emails !

Which ports should I use when setting up email?

The ports you use at this time are ports that belong to mail over a secure connection.

incoming server POP3  :  995
incoming server IMAP via SSL/TLS  :  993
incoming server IMAP via STARTTLS *  :  143
outgoing server SSL  :  465
outgoing server STARTTLS  :  587 - preferred

* this is for older mail clients < windows 8 and, for example, older android versions like KitKat and old iOs systems.

The ports associated with a unprotected connection are:

incoming server POP3  :  110
outgoing server SSL  :  25 of 26

It is better to don't use the above ports, rather use the ports that run through a secure connection.