I'm investigating how exim deliver mails, and I came to the conclusion that when the server is going to send a email exim makes a nslookup and get the higher priority (lower value) MX record and tries to send the mail to the asigned address.
I have my own domain and I always had my MX records pointing to outlook's SMTP, today I tried to add an MX record with higher priority pointing to my vps, I sent an email to that domain and I received it at my vps instead of at outlook, as I expected, alright.
Then I stopped exim service in my vps, expecting that when I send the mail (from another vps) it would nslookup for the next MX record with higher priority, and I would receive that mail at outlook, and exactly, I did, alright.
Then I started the exim service again, I sent another mail expecting that I would receive it at my vps, just like it did before, but no, I got it at outlook instead, even when my vps has higher priority, like if the sender vps would have "blacklisted" it since it failed because I stopped exim service, it didn't even tried to send it (according to /var/log/exim/mainlog), the nslookup directly returned the outlook MX record.
So... has the exim service in sender vps blacklisted that mx record or something? In that case, how can I reverse it?
Is there any way to receive mails in 2 servers? (my vps and outlook), I don't want to forward it, instead, I want the sender to send mails to 2+ servers with same mail address. (I think is not possible, but who knows?)
UPDATE: I sent another mail and now I got it at my vps, but my question still up, and, in case it's blacklisted for many minutes... could I configure it?
What happens if I set two or more MX Records with same priority? I tested it and I received the email at outlook, why? what is the procedure?