Has anybody ever heard of two different laptops suddenly stop sending email to an SMTP server after traveling overseas?
It's a really weird situation. We have two different laptop computers, that have been traveling around Asia for the past three weeks, suddenly fail to access our email server while attempting to send email. They can both download email fine, the problem is only experienced while connecting to the send mail server. The problem only began when the computers returned to the United States and persists using multiple email clients. Nobody else is experiencing email problems in or out of the office.
Any ideas? Can China's government internet monitoring cause some kind of conflict?
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That's strange. Most consumer ISPs that block ports block inbound port 25, not outbound. It's so that their users can't act as smtp servers. I suppose there's something to be said for blocking outbound port 25, only smtp servers should need to talk to other smtp server over port 25.
It would be safer if your send mail server was setup to connect to the sever over a secure connection (ssl/tls) using either port 443 or a custom port number. If you're sending email in the clear on port 25, depending on if you control the open relay issue, you may be sending your username & password in the clear for anyone to see.
I think I my above reply may have been a little confusing. The ISP (Verizon) blocked their inbound port 25 (the port we use for our "send" email server). Our email servicer provided us with a custom port number to use.
In another post, you suggested that ISPs are blocking port 25, among others, as a means to control their customers. Are you suggesting there's another motive than just blocking spam?
Hmm, the only way that makes any sense is if they chose to block port 25 from their consumer customers at the local routers. It's just bad luck that you guys used the same port to deliver emails to your send server (probably the same sever as the receive server). I reitterate that if you have any control over your email server setting that it require ssl/tls to connect. Otherwise all you emails ans usernames/passwords are sent in the clear for anyone to pickup and read, especially at any open wifi spots.
ISPs block ports in order to stop people from using their bandwidth for activities they don't want you doing like serving a website.
I'd expect nothing less, but any mobile platform should act as securely as possible when communicating with the home office. You never know who's listening. I don't want to malign Chinese practices, but if you're taking these laptops overseas and communicating confidential information in your emails, then it needs to be over a secure connection. Any email server you might be using can allow or just require ssl/tls connections. It's just a few changes in settings and a couple opened ports at the server firewall. (If you can look on the laptops, you'll see a checkmark in the email settings for using ssl or tls)
The only reason I'm harping on this is that the smtp port was 25 and that could be configured either way. I wish the standards body would assign a standard port for secure smtp, like 26 or 444 if they aren't in use.