Introduction
If you are seeing one of the following messages from Exim you may be able to gain additional insight about the cause of the issue with the technique outlined below.
exampleuser@exampledomain.tld is undeliverable
exampleuser@exampledomain.tld failed to verify
Procedure
Exim offers the -d flag to increase the verbosity of it's output.
You can add this flag to various address testing commands to gain more information:
exim -d -bv exampleuser@exampledomain.tld
exim -d -bvs exampleuser@exampledomain.tld
exim -d -bt exampleuser@exampledomain.tld