To resolve email not sending out because of the port 25 block at your ISP, you would update the outgoing server port from 25 to 465 with SSL checked.
- Go to Tools --> Email accounts or account settings --> change account --> select your account and click edit or double click the account
- Click on "more settings" and go to the advanced tab
- Change the outgoing server port to 465 with SSL checked
- Go to the outgoing server tab
- Check "my server requires authentication" and "use same settings as incoming".
- Click OK on all windows and try to send mail again.
- Go to Mail -> Preferences --> Accounts and select your account
- In the outgoing server popup menu, select "Edit SMTP Server list"
- Select the outgoing server that you are using
- Switch to the advanced tab under the SMTP server settings
- Change the outgoing server port from 25 or default to 465 with SSL checked.
NOTE: You may receive an SSL warning when using port 465 with SSL checked. Generally you do not want to ignore SSL warnings, however, in this case it is okay to do so. The reason this happens is you're using mail.domain.com (where domain.com is your real domain) for the outgoing server and the SSL is tagged for mailX.u2-web.com (where "X" is a number).