1. ISP customer setup automation sometimes creates issues. Email from domain A to domain B works, but from domain B to domain A doesn't. Be careful if both are customers of the same ISP. Sometimes automated processes create mail domains, DNS zones, and web space for all customers. Customers that use the same ISP can experience issues (depending on mail server software used) if one customer uses ISP mail (POP/IMAP & SMTP) and the other hosts their own mail server. If ISP mail servers have mail domains set up for customers who do not use the ISP provided mail (have their own mail server), when another ISP customer who does use the ISP provided mail service attempts to relay mail through the ISP's mail servers, delivery ends up being server local instead of the server looking up the correct MX record. This usually ends up being an SMTP 550 error (user not found) rejection sent to the sender.

2. Can't send mail to AOL, join the club! If a mail domain can not send mail to AOL, it could be a number of things. The first thing to do is start a telnet SMTP session like the following: [more]

telnet mailin-01.mx.aol.com 25

The AOL server will return an error code and a web link to an article explaining why the mail was blocked. A very common error is 554 (RTR:sc) which means that your sending IP has been blocked due to too many AOL members clicking the "this is spam" link for emails that trace back to you mail server IP or domain. If you are curious about what mail is getting sent on your behalf that is being specified as spam by AOL users, you can create a feedback loop (see http://postmaster.info.aol.com/fbl/). Once you have requested a feedback loop you will be notified when a member clicks "this is spam". The email sent to you from SCOMP@aol.net will contain the complete email and header information. To be removed from an AOL block list, you must call 703-265-4670 and jump through some hoops to be removed. It takes 24-hrs for the removal to take affect.