My users can’t send e-mails, and get the error “553 sorry, that domain isn’t in my list of allowed rcpthosts”

To fix it, do the following:

1. log into your mail server as root;
2. stop qmaild:
# /etc/rc.d/init.d/qmaild stop
3. backup all needed files in the ~vpopmail/etc directory;
4. delete the directory ~vpopmail/etc:
# rm -rf ~vpopmail/etc
5. create it anew:
# mkdir ~vpopmail/etc
6. copy backed files to this new directory;
7. empty the file ~vpopmail/etc/open-smtp:
# cat /dev/null > ~vpopmail/etc/open-smtp
8. start qmaild:
# /etc/rc.d/init.d/qmaild start