Recently, we faced a problem where emails generated from our application were not showing up in AOL inbox(es).

We have recently switched to a new machine & I suspected that for new machine mx-records are not set correctly from where I am trying to send the email.

We didn’t wanted to change our mx-records as we feared loosing any email. This is when SPF works.

http://www.openspf.org

We setup SPf records & this problem is solved. Now, our new machine is a valid email sender for our domain.

But emails were still not making it through AOL.

After some googling & aoling i found this link:

http://postmaster.info.aol.com/trouble/index.html

from here I followed this:

http://postmaster.info.aol.com/tools/telnet.html

I followed the instructions relegiously & got this error:

421-: (DNS:NR) http://postmaster.info.aol.com/errors/421dnsnr.html
421 SERVICE NOT AVAILABLE

URL: http://postmaster.info.aol.com/errors/421dnsnr.html clearly states the problem

So, reverse DNS is not set correctly.

AOL also provides this tool for further testing of your reverse DNS
http://postmaster.info.aol.com/cgi-bin/dns_tool.pl

We asked our hosting provider setup reverse DNS for our domain.

Damnnn.. Why didn’t we first looked at AOL faqs.

Tags: aol dns email smtp spf mx