If the connection to the server on port 25 times out
When you try to send a message, you may see an alert message that messages couldn’t be delivered because the connection to the server on port 25 timed out.
Internet mail servers use port 25 to route messages to each other. Some Internet service providers (ISPs) block port 25 to reduce the amount of junk mail that originates from their domains. By blocking port 25, an ISP requires customers to use its SMTP servers so it can monitor outgoing messages and track down junk mail senders.
Here are things to try if the connection times out:
Ask your ISP if they are blocking port 25 and if you can use any return address, or if you are required to use the address you have with them.
If your ISP is blocking port 25 but not port 587, change the port to 587 and try again. Choose Mail > Preferences, click Accounts, select your website's email account, and then click Account Information. Choose Edit Server List from the Outgoing Mail Server (SMTP) pop-up menu, click Advanced, replace 25 with 587 in the “Server port” field, and then click OK. Try sending your message again.