It doesn't matter what the @query statement is... you can have "Select 1" as the query... if the sys.xp_logininfo SP kicks back an error for the account the agent is...

the issue is with your SQL service not able to "lookup" the AD account... Here is the cmd that DBMail runs:

EXEC sys.xp_logininfo

@acctname = 'Domain\User'

If this command kicks back an...