This question already has an answer here:
I have some problems with my postfix setup. We send newsletter regulaly to our customers once or twice a week. and we have expierenced that many customers do not get their emails, it's simply because our domain has been listed as spammer in their spamfilter.
I've asked one of our customers to check what's the reason that our emails come directly in their spamfilter. he said "the problem is, that we are sending emails from a server which is not registered to be a valid exchanger for domain name [ourdoman].com".
can anyone explain to me what does this mean?
the company use MS exchange as our main mail server. and we use linux / postfix / php to send newsletters. both ms exhcange and postfix share the same domain name.