Outgoing server (SMTP) smtp.office365.com is unknown

Hi,

since a few days I am not able to sent emails using my work email account from my home network.  I receive the error message "Outgoing server (SMTP) smtp.office365.com is unknown".  The SMTP server uses the port 587 and STARTTLS.

It is not an issue with my email client or my account settings nor outgoing mail in general since I am able to sent emails from my laptop at work or from other networks  and I am able to sent emails using my private email account from home.

I also understand that Verizon supports the port 587, thus I am a bit lost as to what the problem could be, especially since it worked before and I have not changed anything.

Any suggestions?

Thanks