More info needed
I have a small process to go through when trying to resolve SMTP issues in osTicket.
First of all, lets try to get info from osTicket on the issue, to do this we go to:
Admin Panel > Emails > select email address
Is osTicket giving you any errors here when you try to commit the SMTP data?
Next, are there any errors coming out of the osTicket logs or PHP error logs?
Hopefully by now you will be able to see what type of issue you have, if it is a simple username/password issue or if there is something like osTicket cannot connect to the SMTP host.
Also, who is the email provider?
Can you please post the information you have plus log info for us to have a look at?
Often the PHP error log will give a clue to why these things stop working.
Cheers,
Ryan