I am currently testing moving isp, i have made the required mx and reverse dns changes and everything checks out. I tried switching over and incoming mail is working fine but we are not sending. I quiclky changed back to the old isp and everything is fine. I noticed in my exchange 2010 server we are using as a send connector (on the organisational configuration/hub transport tabs) the old isp as a mail relay. I'm not familiar with this and have inherited this setup, should i simply disable the external relay to allow outgoing mail to flow?
If not, most server will reject your email.
Also your new Outbound connector must be configure to use MX record and Address space must be SMTP * 1
This is very simple to create by wizard if you have Exchange 2013