I am in charge of a small company's IT department, and am well versed in UNIX/Linux (which our server runs) but not so well versed in Windows (which many of our employees run). We have a website and a mail server hosted at http://www.hostmonster.com/. About a year ago, when the website was made and the server configured, I set up all employees' Outlook to access our mail server using IMAP and SMTP, and there have been no major problems until now.
One of our employees, running Outlook on Windows 7, suddenly reports that his mail will not send, although he can check mail normally. He swears that he "didn't touch anything", and that all he did was visit his parent's house for a week. The problem is not with his router as the mail fails to check at his public library. Upon starting a Windows Remote Assistance session, I was able to determine that while pings to our mail server went through with normal latency, telnet to the server on port 25 fails. The same telnet succeeds on my machine. Moreover, telnet to smtp.gmail.com and mail.comcast.net, as well as a hastily opened port 25 on my home network all fail.
Suspecting a firewall issue, I disabled Windows Firewall as well as Kapersky AV, to no avail. I am currently attempting to contact him again in order to try the suggestions in How to check if a port is blocked on Windows?, but I would like to ask for other ideas as to the source of this problem or any possible suggestions.
Thank you very much.