Mail sending error (Unable to relay)

[TCap112]

Description

When i am sending a mail via SMTP to a Mail-adress with another domain than the senders one, i receive this error:

mail.psi.de:25 [] Failed to add recipient: @localhost [SMTP: Invalid response code received from server (code: 501, response: 5.5.4 Invalid Address)] and also: #< #5.7.1 smtp;550 5.7.1 Unable to relay> #SMTP#

The SMTP Server receives the mail, but can't relay it.

the weird thing is that sometimes it works and sometimes it doesn't.

Is there any known issue which could cause this?
Or is it possible that it's a problem with the SMTP Server/hosting Server?
Maybe the SMTP Server marks it as spam?

Versions

v1.10.1
Windows 10 OS
Tried with Firefox/Chrome

Unfortunately, i can't upgrade my osTicket since i have made alot of changes in the sourcecode, that i don't want to lose.

[JediKev]

@TCap112

Unfortunately, 1.10.x is EOL and no longer supported. You’ll need to upgrade to 1.14.x or 1.15.x to receive any support/assistance. Otherwise you can post on our Forum to receive assistance from the community.

Cheers.

[ramrajone]

code: 501, response: 5.5.4 Invalid Address

It may be a bad email address, that's that your error code says

Also, side note, the longer you stay with the older version harder it will get to upgrade, best thing is to clone the current server setup and upgrade on a test server with your changes to source code