Hi!Thanks for your suggestion, but I don't think that the mailserver is forcing TLS/SSL.I installed Thunderbird mailclient and configured it for IMAP, no transport-security and NTLM as authentication-method. If I disable TLS 1.0 on the mailserver, Thunderbird is still able to connect. But osTicket is throwing the error.In the IMAP-log on the mailserver I can see the starttls command if connecting from osTicket:#Fields: dateTime,sessionId,seqNumber,sIp,cIp,user,duration,rqsize,rpsize,command,parameters,context2018-08-23T07.513Z,0000000000000001,0,10.3.1.12,10.3.1.133,,-2147483648,0,53,OpenSession,,2018-08-23T07.887Z,0000000000000001,1,10.3.1.12,10.3.1.133,,187,19,151,capability,,R=ok2018-08-23T07.965Z,0000000000000001,2,10.3.1.12,10.3.1.133,,0,17,40,starttls,,Connecting from Thunderbird looks like this:#Fields: dateTime,sessionId,seqNumber,sIp,cIp,user,duration,rqsize,rpsize,command,parameters,context2018-08-23T07.705Z,0000000000000002,0,10.3.1.12,10.2.16.150,,-2147483648,0,53,OpenSession,,2018-08-23T07.705Z,0000000000000002,1,10.3.1.12,10.2.16.150,,0,12,144,capability,,R=ok2018-08-23T07.137Z,0000000000000002,2,10.3.1.12,10.2.16.150,helpdesk,3182,41,333,authenticate,NTLM,"R=ok;RpcC=20;RpcL=15;LdapC=22;LdapL=16;Msg=""User-71a9-4a3b-a08f-db39d0cca9e0-M.server.com"";Budget=""Conn,HangingConn,AD:$null/$null/0%,CAS:$null/$null/5%,AB:$null/$null/0%,RPC:$null/$null/1%,FC/0,Policy-0f33-4e00-a7d7-3fbda2c32a26,Norm"""Any suggestions? Where in osTicket would ist be possible to force encryption? Maybe one of my fellow admins did tinker with this setting...Cheers,Lukas