Error messages when sending emails

It can happen that you get an error message when sending emails or setting up an email account. This error message shows a specific problem that prevents the email from being sent.
These error messages appear in the top right via a pop-up. In addition, a notification is created for it. You can click that notification open to see more details about the error message.

Every error message consists of 4 blocks:

1. Title: here you see which document this error message relates to
2. Detail: you see the error message explaining why the email could not be sent.
3. Concerning: you see which email this error message relates to. You can also click through from here.
4. Help: you get a link to the helpdesk page where you can find more information about your error message

Most common error messages when sending emails

**Authentication error 5.7.3. ** ****
Incorrect use of username or password. Set up the correct details again.

Couldn't connect to host, port: smtp-auth.mailprotect.be, 995; timeout 60000; nested exception is: java.net.SocketTimeoutException: connect timed out:
We cannot connect to the server. The port of the SMTP connection is wrong. Set up the correct port.

User doesn't have rights to send e-mail:
When using an Office account, you have to sign in with the same email address as the 'from email address' on the account. With this error message that is not the case.

The e-mail is too large to send because of the attachments:
Your attachments together are too large for the mail server. Send the attachments in several emails, or leave out one large attachment and share it another way. With an Office 365 account you get this message in plain language; with other account types the message can come from your own mail server and look more technical.

Microsoft could not attach the file to the e-mail. Please try sending again:
You only get this message with an Office 365 account, and only for large attachments. Attachments from 3 MB up are uploaded to Microsoft in chunks; if something goes wrong there, the attachment does not get linked to the email. Robaws automatically tries up to three times. If you see this message, all of those attempts failed and the email was not sent. Simply send it again: that usually works. If it keeps failing, reduce the size of your attachments, for example by sending the email in several parts. The problem mainly occurs when you attach several large files at once.

E-mail could not be delivered

Sometimes an email does leave, but the recipient's mail server rejects it afterwards. If the email goes through the Robaws mail server, and so not through your own Office 365, Gmail or SMTP account, you then get the notification E-mail "…" could not be delivered, with the subject of the email in the title. This applies, for example, to the UBL that Robaws sends to the digital mailbox of your accounting software.

For each email address you see whether the problem is temporary or permanent, and why: for example because the mailbox is full, the address does not exist, an attachment was rejected or the recipient reported the email as spam. If the mail server only reports that it refused the email, the notification also shows the Cause where possible, for example 'the mailbox does not exist' or 'the domain does not exist or does not accept e-mail'. Under Reply from the mail server you also read word for word what the recipient's mail server replied, for example '550 5.1.1 user unknown': that often names the actual problem. From the notification you open the email in question. The notification goes to whoever sent the email; for an automatic email, everyone with administrator rights gets it.

• Check the email address with the recipient, correct it where needed and send the email again. If the mailbox is full, try again later.
• If the mail server refuses the email permanently, Robaws no longer sends to that address. Later emails then also get the message that Robaws no longer sends to this address. In that case, check the address with the recipient first: as long as their mail server refuses the email, unblocking it is pointless. If the address is correct and the problem has been solved on the recipient's side, contact support@robaws.com to have it unblocked.

Updated on: 02/11/2026