550 Authentication is required for relay - 550 not local host
This can be due to one of the following reasons:
- This error is most often associated with NOT having the box checked for "My server requires authentication". Check this box and then try sending.
- Another cause of this error is that your Internet Service Provider (such as AOL or MSN or Cox) may require that you use THEIR own SMTP server to send email. You will need to check with them. If this is the case, you may or may not also need to check the "authentication" box.
NOTE: If you are using "mail.your_domain_name.com" (using your domain name) for the SMTP server, make sure that the check-box at the bottom of the screen is checked (My server requires authentication).
421 Service Not Available
On an error related to Remote host said: 421 SERVICE NOT AVAILABLE email AOL rejected, there is some times an additional description right below that. Look for that first and if that doesn't help, then you should contact AOL regarding this error as it is generated on their end. Please ask them for the specific reason it was rejected. Then let us know if it is something we can help correct.
Unexplained Undeliverable Messages
If you're receiving several emails mentioning "undeliverable" in your inbox for email addresses you have never sent to, your email account may have been compromised due to a weak password. You will need to strengthen the password for your email account to prevent further unauthorized usage (a strong password will need to be at least 8 characters in length including an upper and lowercase letter, a number and a symbol)