ntozier, my apologies, you are quite correct ! Having nothing to go on will not help my cause what so ever ! .... So, here are some details which may help enlighten us both :-)Server InformationosTicket Version v1.10.1 (9ae093d) — Up to dateWeb Server Software Apache/2.4.33 (Unix)MySQL Version 10.1.27PHP Version 7.0.30Example Error Message from OsTickets:Mailer ErrorUnable to email via SMTP.sys3internet.net Failed to set sender: support@sys3.com IP Address.84.57.154Entry in SMTP In LOG File (user/pass starred out)Tue 2018-07-10 10.813: Session 430151; child 0003Tue 2018-07-10 10.813: Accepting SMTP connection from 91.84.57.154 to 84.22.183.37Tue 2018-07-10 10.815: --> 220 smtp.sys3internet.net ESMTP MSA MDaemon 15.0.3; Tue, 10 Jul 2018 10 +0100Tue 2018-07-10 10.826: <-- EHLO orwellTue 2018-07-10 10.826: --> 250-smtp.sys3internet.net Hello orwell, pleased to meet youTue 2018-07-10 10.826: --> 250-AUTH LOGIN PLAINTue 2018-07-10 10.826: --> 250-8BITMIMETue 2018-07-10 10.826: --> 250-ENHANCEDSTATUSCODESTue 2018-07-10 10.826: --> 250-STARTTLSTue 2018-07-10 10.827: --> 250 SIZETue 2018-07-10 10.837: <-- AUTH LOGINTue 2018-07-10 10.837: --> 334 VXNlcm5hbWU6Tue 2018-07-10 10.849: <-- ******Tue 2018-07-10 10.849: --> 334 UGFzc3dvcmQ6Tue 2018-07-10 10.860: <-- ******Tue 2018-07-10 10.861: --> 235 2.7.0 Authentication successfulTue 2018-07-10 10.861: Authenticated as support@sys3internet.netTue 2018-07-10 10.871: <-- RSETTue 2018-07-10 10.872: --> 250 2.0.0 RSET? Well, OKTue 2018-07-10 10.882: <-- MAIL FROM: <support@sys3.com>Tue 2018-07-10 10.883: --> 250 2.1.0 Sender OKTue 2018-07-10 10.893: <-- RCPT TO:<support@sys3.com>Tue 2018-07-10 10.895: --> 250 2.1.5 Recipient OKTue 2018-07-10 10.905: <-- DATATue 2018-07-10 10.906: Creating temp file (SMTP): d:\mdaemon\queues\temp\md50001214275.tmpTue 2018-07-10 10.906: --> 354 Enter mail, end with <CRLF>.<CRLF>Tue 2018-07-10 10.990: Message size: 526508 bytesTue 2018-07-10 10.002: Message creation successful: d:\mdaemon\queues\inbound\md50028261922.msgTue 2018-07-10 10.002: --> 250 2.6.0 Ok, message saved <Message-ID: <330470096l.1303950734l138671440l1236l@sys3.com>>Tue 2018-07-10 10.009: <-- QUITTue 2018-07-10 10.009: --> 221 2.0.0 See ya in cyberspaceTue 2018-07-10 10.009: SMTP session successful (Bytes in/out: 526645/539)Both tmp and msg files no longer exist and when looking in these directories in real time, they immediately get deleted once they have been processed.Orwell is the name of our mailserver. The mail server we use is MDaemon.I have checked the IP address given in several instances of the error and they all seem to be owned by our old hosting company which was bought out by heart (i think). I know we recently whitelisted our domains which enabled mails to flow but I'm thinking there might be something else adrift. As I monitor the error logs in OSTickets, they increase but not when a ticket is submitted, which makes me think that it is another SMTP interaction causing this. Currently, if a user replies, it goes to an address which is not being picked up by OSTickets but simply to an email alias. I think that there are two things going wrong here. Firstly, I need to give OSTickets an email address and account to pickup reply emails from and/or if OSTickets is already doing this and this is the cause for the error, how can I change the email address to see if the error message in OS changes and to then sort out the new email account which I think it needs.I hope this makes sense and feel free to say I'm talking rubbish as its all randomly going through my head at the moment but I think this is where I am at !thanks for all and any help.Sam