LMTP error in newest Dovecot

After upgrading from Dovecot 2.2.29.1 to 2.2.30.1, one of my users email account have this error in the log (I have masked the email address and user):

2017-06-05 17:23:20 Received from username@host.name.tld U=user-removed P=local S=3314 id=xxxxx@www.domain.tld T="subject-removed"

2017-06-05 17:23:20 email@address.tld R=virtual_user T=dovecot_lmtp_udp defer (-44): LMTP error after RCPT TO:<email@address.tld>: 451 4.3.0 <email@address.tld> Internal error occurred. Refer to server log for more information.

So far this only happen to this one user. I have not seen it on any other email addresses. Have anybody else seen this happen? I don't find anything else in the logs.

By the way I am ruing the newest exim.conf and dovecot.conf.