A couple of months ago some of our emails got hacked (they got hands on the passwords) and they sent out 1000+ spam emails from those specfic accounts to random adresses. Now months later after having the hack problem fixed, the email accounts still face outgoing mail errors. Not with all emails, some get sent fine others will be blocked.
For instance some of the errors we get are:
Error example 1
href="mailto:email@example.com">firstname.lastname@example.org host s01.spamexperts.axc.nl [18.104.22.168] SMTP error from remote mail server after end of data: 550 To contains invalid characters.
Error example 2
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
email@example.com host s01.spamexperts.axc.nl [22.214.171.124] SMTP error from remote mail server after end of data: 550 To contains invalid characters.
Error Example 3
Reporting-MTA: dns; vserver87.axc.nl
Action: failed Final-Recipient: rfc822;Txxx@xxx.com Status: 5.0.0 Remote-MTA: dns; s01.spamexperts.axc.nl Diagnostic-Code: smtp; 550 Maximum line length exceeded (see RFC 5322 2.1.1).
Error Example 4
Reporting-MTA: dns; vserver87.acx.nl
Action: failed Final-Recipient: rfc882;firstname.lastname@example.org Status: 5.0.0 Remote-MTA: dns; s01.spamexpers.axc.nl Diagnostic-Code: smtp; 550 Maximum line length exceeded (See RFC 5322 2.1.1)
We are getting kinda desperate here to get this problem fixed because we don't know what to do anymore.
If it matters everything is hosted on Versio.nl
Does anyone has any clue what is going on with the emails and/or has an idea on how to fix the issues?