If you are unable to send email from your iPhone but can receive email, please check the following troubleshooting steps below.
1. Touch the Settings icon
2. Go to Mail > Contacts > Calendars
3. Click on the email account
4. Click on your email address under the "IMAP" heading
5. Scroll to the bottom where you will see "Outgoing Mail Server"
6. Click on the SMTP server and ensure you are using the following settings:
Hostname: <your domain>
Username: <your full email address>
Password: <your email password>
Use SSL: On
Authentication: Password
Server Port: 587 (if you have already used port 25 and still you cannot send email out)
To ensure that you have the correct email password, you may try accessing your email via Webmail to verify if it is working. In case you cannot log in with the password that you use, we suggest that you log in to your Plesk Panel and reset your email password. Then go back to your iPhone settings and enter the new email password.