SMTP error from remote mail server after RCPT TO: 451

[Mike1]

Hello

I've noticed that some emails that we send are not delivered. The same recipient get's email from two persons in the office when another person sends an email it's not being delivered with this message:
SMTP error from remote mail server after RCPT TO: 451

I've checked and it's actually fine when sending an email from web client, but it fails when sending from Outlook 2016 with IMAP/SMTP connection.

Any ideas what might be causing this issue?

Thanks

 

[cPanelLauren]

Sounds like it could be a configuration or network issue. How's the mail client setup? Did you use the mail client configuration tool available in cPanel?

 

[Mike1]

Thanks for your reply.

I set up all the Outlooks manually. Another user tried to email that particular person and it failed with the same message - that was from different PC and Windows Live Mail.

I can see it works now for someone that it didn't work before, I think the only thing I've done was disabling a Bitdefender Anti-Ransomware tool - I didn't think that would affect emails - I'll do some tests and post an update.

 

[cPanelLauren]

Hi @Mike1


bitdefender could produce the behavior you're seeing it is common with anti-virus software to cause issues with a mail client's ability to send/receive mail. Do let us know if that was the cause!

Thanks!