Mandrill is giving me "Sender address rejected: Domain not found" when sending emails to nauta.cu

Question

I have my Mandrill account sending emails to many clients. The ones using addresses of the type [email protected] are not receiving any emails at all, and when I go to Mandrill it says:

Nov 8, 2015 11:39 pm 450 4.1.8 : Sender address rejected: Domain not found Sent from: 198.2.178.1 Sent to: 181.225.231.50

When I send an email from my gmail to that nauta.cu account, it works. Also, if I send an email from Mandrill to my gmail account it works too.

This is the result of an nslookup for nauta.cu

nslookup nauta.cu Server: 127.0.1.1 Address: 127.0.1.1#53

Non-authoritative answer: *** Can't find nauta.cu: No answer

This is super important and time-sensitive for my company. I have been struggle for days, and I really appreciate any clues that lead me on the right way.

Answer 1

You have to set up a sending domain as explained here: https://mandrill.zendesk.com/hc/en-us/articles/205582387-How-to-Set-up-Sending-Domains . More background discussion about the topic is here: http://blog.mandrill.com/we-are-making-domain-verification-mandatory.html .

For time sensitive issues, I would suggest reaching out to Mandrill Support. They are very prompt in responding. For reaching to Mandrill support, you just have to log into mandrillapp.com and click on Support button on the left bottom side of the page.

Hope this helps,

Answer 2

The MX records for nauta.cu currently resolve to mail2.etecsa.net and mail3.etecsa.net, but the IP address that Mandrill tried to resolve in your example was 181.225.231.50. That IP was tied to mx2.etecsa.net, but is no longer in use by nuata.cu. So when Mandrill first tried to deliver your email to nauta.cu, it was likely during the time when the old MX record (181.225.231.50) was still cached, and before the new ones had fully propagated.

This is probably resolved now since the TTL on nauta.cu's MX records is so low, but Mandrill's servers are likely retrying delivery for some time until the emails ultimately bounce, and then they'll stop trying to send those same emails. For example, when a receiving SMTP server (nauta.cu's in this case) returns a 4xx type of error, most sending servers (like Mandrill's) will retry delivery for a set period of time before giving up. You'll probably end up having to manually re-send these emails if you want them to get through, instead of waiting for Mandrill to bounce them.