Sending email from hotel or remote connection

Question

For some reason, using pop email account and having password auth. "on" I can receive emails when at a remote hotel connection but cannot "send" any emails out?
I have contacted isp and they say with password on, should be working???

Answer 1

It all depends on the policy of whoever is the ISP at each location and the method used by the outgoing (SMTP) server to determine whether you’re a legitimate user. Note that when you’re not at home, the ISP at that location is usually not the same as the ISP when you’re at home.
In an attempt to fight spam, many ISPs restrict the ability to send using an outgoing (SMTP) server not owned by them, usually by blocking port 25 for all traffic outside their own network, which means you cannot send with an SMTP server not owned by them if configured to use that port number. And it may happen the other way around as well, i.e. the outgoing server itself may look at the IP address you’re connecting from and refuse the connection if you’re outside its own network.
Something that often works is changing the outgoing server port to 587 (or whatever alternate port number the outgoing server listens to) instead of 25 and using some form of authentication in Preferences > Accounts > Account Information > Outgoing Mail Server > Server Settings, but two conditions must be satisfied for this change to work: (1) the ISP must not block that port as well AND (2) the outgoing server in question must listen to that port and accept a form of authentication not based on the IP address you’re connecting from.
Independent mail service providers not tied to a particular ISP, such as .Mac and Gmail, do allow authenticated SMTP access on port 587, which is the reason changing the outgoing server port number solves the problem for them if the ISP doesn’t block that port as well.
The following article, for example, describes several ways to address this issue in the case of .Mac, but can be useful for other mail accounts as well (not just .Mac), and applies to all versions of Mac OS X (not just Mac OS X 10.4.2 and earlier as the article states):
.Mac: Server timeout alert message when sending email