MWEB Outgoing Mail

[Tinuva]

Technically the gmail smtps server should work on all networks, unless they only give you access via a proxy server, and then have their own SMTP server which have access to send email.

 

[PsyWulf]

You are facing a few problems here which i'll try to list

1) Sending mail using either Authenticated or Anonymous smtp servers
Anonymous smtp usually requires you to be on the same network as the server you are trying to use

I'm a client for ISP x so I can use ISP x's anonymous smtp but not ISP y or vice versa

Authenticated smtp requires you to authenticate to identify yourself as an authorized user of the Authenticated smtp server

I'm a client of ISP x,so I can use ISP x's authenticated server on any network if I authenticate first

2) Some ISPs stealth redirect commonly used SMTP ports to their smtp servers
Port 25 usually is redirected,so if your actual SMTP is anonymous and the redirect smtp is anonymous it'll work,if you use authentication and they don't it'll fail

3) Some ISPs block port25 except to their own Anonymous smtp
Pretty self explanatory

4) Some Internet providers ( Cafe,Hotel ) might have a proxy in place that prevents traffic to some ports
If you can't access the SMTP port your server requires,well too bad

Generally,your "most" fault-free option is using an authenticated server using SSL ports,it's the least blocked/redirected option