Hi, I have added our domain to Mail module using all steps necessary to verify domain... However, some users/email addresses are not using our Onlyoffice service. We are finding issues to end them messages. There is Undelivered Mail Returned to Sender error:
This is the mail system at host mail.onlyoffice.eu.
I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster. If you do so, please include this problem report. You can delete your own text from the attached returned message.
The mail system
<email@example.com>: user unknown
What is funny, they can send us a message
Any ideas how to manage it?