friend of mine got an error message from qmail: Sorry,_no_mailbox_here_by_that_name._(#5.1.1)/
and here is what i adviced, it might be usefull for someone.. :

i checked /var/log/kloxo/maillog (tail -n300 /var/log/kloxo/maillog)

and found this:

Mar 23 21:09:31 * qmail: 1395601771.973375 delivery 25: failure: User_and_password_not_set,_continuing_without_auth entication./<*@gmail.com>_173.194.*_failed_after_I_sent_the_me ssage./Remote_host_said:_550-5.7.1_[107.182.*_______1]_Our_system_has_detected_an_unusual_rate_of/550-5.7.1_unsolicited_mail_originating_from_your_IP_ad dress._To_protect_our/550-5.7.1_users_from_spam,_mail_sent_from_your_IP_addr ess_has_been_blocked./550-5.7.1_Please_visit_http://www.google.com/mail/help/bulk_mail.html_to_review/550_5.7.1_our_Bulk_Email_Senders_Guidelines._sm4si 15596479obb.4_-_gsmtp/

as you can see, recipient server (gmail) dont allow delivery of your email because detected unusual rate of emails, check the link they proveded you

But that is not issue you you asked about. You asked about [email protected] delivery failure

Your maillog file tells:

Mar 23 21:09:29 * qmail: 1395601769.663076 starting delivery 27: msg 36504396 to local [email protected]
Mar 23 21:09:29 * qmail: 1395601769.663093 status: local 1/10 remote 1/60
Mar 23 21:09:29 * qmail: 1395601769.665037 delivery 27: failure: Sorry,_no_mailbox_here_by_that_name._(#5.1.1)/

Mar 23 21:09:29 * qmail: 1395601769.727135 starting delivery 28: msg 36504392 to remote [email protected]
Mar 23 21:09:29 * qmail: 1395601769.727169 status: local 0/10 remote 2/60
Mar 23 21:09:29 * qmail: 1395601769.750562 delivery 28: failure: Sorry._Although_I'm_listed_as_a_best-preference_MX_or_A_for_that_host,/it_isn't_in_my_control/locals_file,_so_I_don't_treat_it_as_local._(#5.4.6)/

i googled above error and there is an advice from Anton Akola regarding that: http://forum.parallels.com/showthread.php?73883-qmail-local-delivery-to-root-failures&amp;p=314182&amp;viewfull=1#post314182
I checked mentioned "locals" file on your VPS and it appears it contains only "localhost" so i assume adding your hostnames (mail.yourhosteddomain.com also) line by line may help. Then restarting qmail (service qmail restart)

Also there is a good advice: http://serverfault.com/a/449317
(but might not be related to the issue, its another case)

hope that point you to right direction

PS: there are scripts in Kloxo like /script/fixmail ; /script/fixpop i think, but im littlebit afraid to use them to not mess the things, but it may also help