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If you aren't able to send email, this usually means one thing... your internet provider is blocking you from using anyone's outgoing mail servers but their own. Many major internet service providers (ISPs) block outgoing emails to prevent their internet connection from being used for spam. In order to work around this issue, we have opened Port 26. Please change the outgoing mail server (SMTP) from the default Port 25 to Port 26.
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. The filter can create problems for e-mail servers and block legitimate e-mail as well as spam. When an e-mail client that runs on your computer delivers messages, it always uses port 25 to transmit data to remote e-mail servers. Therefore, if your ISP is blocking the port, your messages will not get through.
The ISPs that block port 25 require their SMTP server to be used instead of the remote SMTP server.
Some ISPs that block port 25 include:
- Charter mails
- People PC
- Comcast ATTBI
If your ISP is on this list or you believe port 25 is blocked, please see our related article for information about changing the outgoing SMTP port from 25 to 26.
What if both Port 25 and Port 26 don't work?
Some ISPs block both ports, and you will need to follow your ISP's procedures for sending email. You will typically have one or two choices. Sometimes you may contact your ISP to request that they open port 25, and they will do this for you, although many ISPs have begun declining to do so. Some ISPs may require you to use their SMTP servers for all outgoing mail, so that they can monitor outgoing email on their network in order to prevent spam.
You'll want to contact your ISP about which SMTP servers you should use for outgoing email. This information is usually posted on a page of their website. If they have a search box on their site, searching for "port 25" will usually lead you to the relevant pages.
You may still send email as being from your domain (i.e. firstname.lastname@example.org); it just needs to be routed through their SMTP servers.
But my mail used to work.
Sometimes ISPs change their policies and start implementing blocks to certain ports without informing their customers (other than perhaps a post on their website). Most ISPs post information about Port 25 on their website if they have implemented a policy of blocking it. If sending mail suddenly stops working, this is probably why.