Some Internet Service Providers in an effort to curb spam coming from their networks have completely blocked outbound traffic on port 25 except for their own mail servers. There is a quick test to see if this is happening for you.
We need to open a command line interface. In Windows you can click on Start -> Run and type cmd.exe. In OS X you can click on Applications -> Utilities -> Terminal.app Once you are at a prompt, type
telnet smtp.mxtoolbox.com 25
If you are not blocked you should see something like this
Trying 208.123.79.51...
Connected to smtp.mxtoolbox.com.
Escape character is '^]'.
220 smtp.mxtoolbox.com ESMTP
If you do, then you can type 'quit' and it will close the connection. Congratulations, you are not blocked. If you get a message about connection refused or anything similar, then you can test our workaround, which is to use port 2525. From a prompt type
telnet smtp.mxtoolbox.com 2525
You should now be able to connect. If so, then when you are configuring your mail client, change the Outgoing SMTP port to be 2525 instead of 25. If you still cannot connect, you should contact your local IT admin to see what the problem is. The probable cause will be a router/firewall blocking your connection, or Firewall / AntiVirus software.
Peter
Product Development Engineer
peter@MXToolBox.com
512-637-8762