5.7.1 client was not Authenticated

good day

hope some1 can help me i have semilar problem on the 5.7.1 error

but this time its only for 1 user,the user can get mails but when he sends a mail out with bulk statements in the ProgramSAP that we use,he is the only user that gets this 5.7.1 error.

and the Anonymous user in permission groups are selected

if some 1 can help me pls