our dev wrote a script that'll send an email externally but it bounces with the following error:
smtp;550 5.7.1 Unable to relay> #SMTP#
Your message wasn't delivered due to a permission or security issue. It may have been rejected by a moderator, the address may only accept e-mail from certain senders, or another restriction may be preventing delivery.
It works fine if I want to send the email internally tho. The server is on the allowed list on the receive connector and anonymous users is checked in the permissions groups tab
using exchange 2010 SP3