Different email addresses of same email server for sending and receiving

Question

I am actually a fresher in terms of configuring an email server. Recently I configured a Postfix email server combining with dovecot and squirrelmail on AWS EC2 centos server, following this guide:

How to configure an email server

The problem I am facing is that, when I send an email using the mail server that I have configured on external emails like outlook, gmail etc. is sent using the following email address

noreply@example.app.

But, I cannot send an email to the above-mentioned address using outlook or gmail because the sender shows me this error: Gmail Error Description

But once I send the email after modifying the above-mentioned email address to the following: noreply@mail.example.app, I receive an email on my configured email server. What I want is that both the sender and receiver email addresses should be: noreply@example.app Here are my DNS records for the domain: DNS

Below is my Postfix Master.cf File: '''

smtp      inet  n       -       n       -       -       smtpd
587      inet  n       -       n       -       -       smtpd
submission inet n       -       n       -       -       smtpd
  -o syslog_name=postfix/submission
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_recipient_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING
smtps     inet  n       -       n       -       -       smtpd
  -o syslog_name=postfix/smtps
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_recipient_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING
pickup    unix  n       -       n       60      1       pickup
cleanup   unix  n       -       n       -       0       cleanup
qmgr      unix  n       -       n       300     1       qmgr
tlsmgr    unix  -       -       n       1000?   1       tlsmgr
rewrite   unix  -       -       n       -       -       trivial-rewrite
bounce    unix  -       -       n       -       0       bounce
defer     unix  -       -       n       -       0       bounce
trace     unix  -       -       n       -       0       bounce
verify    unix  -       -       n       -       1       verify
flush     unix  n       -       n       1000?   0       flush
proxymap  unix  -       -       n       -       -       proxymap
proxywrite unix -       -       n       -       1       proxymap
smtp      unix  -       -       n       -       -       smtp
relay     unix  -       -       n       -       -       smtp
showq     unix  n       -       n       -       -       showq
error     unix  -       -       n       -       -       error
retry     unix  -       -       n       -       -       error
discard   unix  -       -       n       -       -       discard
local     unix  -       n       n       -       -       local
virtual   unix  -       n       n       -       -       virtual
lmtp      unix  -       -       n       -       -       lmtp
anvil     unix  -       -       n       -       1       anvil
scache    unix  -       -       n       -       1       scache

Below is my Postfix Main.cf

queue_directory = /var/spool/postfix

command_directory = /usr/sbin

daemon_directory = /usr/libexec/postfix

data_directory = /var/lib/postfix

mail_owner = postfix

unknown_local_recipient_reject_code = 550

alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases

debug_peer_level = 2

debugger_command =
     PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin
     ddd $daemon_directory/$process_name $process_id & sleep 5

sendmail_path = /usr/sbin/sendmail.postfix

newaliases_path = /usr/bin/newaliases.postfix

mailq_path = /usr/bin/mailq.postfix

setgid_group = postdrop

html_directory = no

manpage_directory = /usr/share/man

sample_directory = /usr/share/doc/postfix-2.10.1/samples

readme_directory = /usr/share/doc/postfix-2.10.1/README_FILES
myhostname = mail.example.app
mydomain = example.app
myorigin = $mydomain
inet_interfaces = all
inet_protocols = all
mydestination = $myhostname, localhost, $mydomain
mynetworks = 127.0.0.0/8
relay_domains = $mydestination
home_mailbox = Maildir/

Answer 1

This is a DNS issue. You have a wrong a MX record, i.e. your domain example.app doensn't have an MX record (mail.example.app has an MX record instead, but it doesn't need it). Thus Gmail tries to direct mail to A record (as a fallback).

Add into example.app zone the following record:

example.app. MX 10 mail.example.app.

(and remove the mail.example.app MX, it does no harm, but it doesn't needed)

this will tell the world that mail for example.app domain is processed at mail.example.app and after obvious negative DNS caching timeout Gmail and others will deliver mail to your mail server.