Why outgoing mail to the external network does not work. Exchange 2010?

Question

Email

Good day.
Please tell me, I've been struggling with this problem for a week now, but there is not enough qualification.
Mail messages accumulate in the waiting queue on the mail server with error 451 4.4.0 and explanation 421 4.2.1
This happened after the IP address of the mail server was changed.
What was done:
On the domain controller in DNS, all records are correct, the superior specialist corrected the addresses on the router that looks outward, all the settings on the Exchange network were also corrected.
A full backup using VSS was made, old transaction logs were cleaned out and the database was defragmented.
Telnet from the mail server connects to external addresses on port 25 without any problems
Just in case, a request was made to the provider (MTS), which assures that it does not block ports.
Tried to make mail transportation through external public DNS.
I found advice on the net that the GUID on the network adapter can fly off. Checking such errors did not reveal.
2 DNS servers located on domain controllers were checked (NS servers are located on these CDs), they replicate without problems, all zones correspond to each other, communication between them goes on.
All these options did not help.
I just don't know where else to dig.

Answer 1

check send connectors. if they are default, then it is easier to recreate them.

Set-TransportServer -Identity <имя сервера> -ExternalDNSAdapterGUID <GUI нужного адаптера из Get-NetworkConnectionInfo>

- it is necessary if the network card changed in the server. Ex remembers everything that sticks out in it and sends mail based on past settings.

Answer 2

First oddity: Two sendconnectors with AddressSpaces : {SMTP:*;1} - both have Verbose Logging disabled (off - enabled) the ability to relay from a new IP Exchange is enabled.
The recommendation is to enable verbose logging on both, to make a test session for sending emails. Find the session in the log, filter by id, finally understand who is chopping mail.