Weird mail issue, can’t connect from some locations

I've had this issue since I moved my website from ServerA to ServerB about 3-4 months ago.
There's 2 locations (my home and my GF's home) where I cannot setup the email on a 3rd party client (IE; Thunderbird, Outlook or on my phone). When I try to enter all the information, it sets at "connecting to server" and then comes back saying it cannot connect.
But, if I go to another location (IE; Work) and try to set it up with the exact same information, it connects without any issues.
Once the…
Weird mail issue, can't connect from some locations

See original post by killaklown