smtp2go postfix

 smtp_generic_maps = hash:/etc/postfix/generic #this file us used to change domain or username

smtp_sasl_auth_enable = yes

smtp_sasl_password_maps=static:asterisk-voip.com:QzNanBj4r

smtp_sasl_security_options = noanonymous

mtp_tls_security_level = may

header_size_limit = 4096000

relayhost = [mail.smtp2go.com]:2525

relay_destination_concurrency_limit =20

//////////////////////////////

if you want to   change   domain or username

add to the end of this file   /etc/postfix/generic

# this content

root@asterisk-voip.com studio@asterisk-voip.com


---------

add the config    with this command 

postmap /etc/postfix/generic

----

restart

service postfix restart

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test   echo 'Test email' | mail -s 'This is a test July' ambiorixg12@gmail.com

check logs  /var/log/maillog

https://www.cyberciti.biz/tips/howto-postfix-masquerade-change-email-mail-address.html