If you try to send out mail through our mail server (mail.your-domain.com or your-domain.com) and find that you get an error or messages sit in your outbox, it could be that your Connectivity ISP is blocking this mail from being sent by blocking 'Port 25.' If you are having this problem, please see instructions to fix, or read below for more detailed background information.
Why are they blocking Port 25?
Many ISPs are blocking what is called "Port 25" which is the port used to send e-mail. They are doing this to cut down on the amount of spam that is sent from their networks. All e-mail sent via the Internet is routed through the port 25, the channel used for communication between an e-mail client and an e-mail server. Even though port 25 blocking will probably become an industry standard, however, the filter can create problems for e-mail servers and block legitimate e-mail as well as spam.
Port 25 blocking allows ISPs to block spam sent out through their networks, but it tends to punish the innocent that have a need to send through e-mail servers other than those belonging to their ISP. The ISPs that block port 25 require their SMTP server to be used instead of the remote SMTP server or a SMTP server running on your computer.
Some ISPs that block Port 25
AT&T MindSpring ATTBI
Instructions to fix
You should change your email software to use Port 26 instead of 25. Alternatives are also 487, 587. Be sure you are changing your outgoing SMTP port setting (as opposed to your incoming POP/POP3/IMAP setting). This entire discussion assume non-SSL. (Use a different port number for SSL, which is rarely needed)
Note: Remember if you haven't checked mail in the past 10 minutes and try to send through our server, it won't send. Simply check your mail then try and send again.
Outlook 2007: Tools> Account Settings> (double click email address account) > More Settings...> Advanced Tab>
Edit the field: Outgoing server (SMTP): __26____
Outlook 2002: TOOLS > EMAIL ACCOUNTS > VIEW OR CHANGE > Select your Account then CHANGE > MORE SETTINGS > ADVANCED > Change outoing port to 26.
Outlook Express: TOOLS > ACCOUNTS > Click on Mail Account then click on PROPERTIES. Go to the ADVANCED tab and change 25 to 26.
Go to Edit > Mail & Newsgroups Account Settings from the menu.
If necessary, click the symbol next to your account name to expand the list of options.
Click on Server Settings.
Change the SMPT/Outgoing server port from 25 to 26.
Netscape 6: EDIT > MENU > PREFERENCES > Click on the Mail Server on Left then EDIT > change your Outgoing Mail server to: mail.your-domain-here.net:26
In Eudora 5.1 or older:
1. Close Eudora.
2. Look in the Eudora directory (probably c:\program files\qualcomm\eudora)
3. In the directory "extrastuff" you will find a file called "esoteric.epi". Drag it to the main Eudora folder.
4. Start up Eudora
5. Go to Tools -> Options -> Ports
6. Type port 26 in the box for SMTP port.
Port Settings information for Macs: www.cruzio.com/index.php?option=com_smf&Itemid=38&topic=293.0