I upgraded the Domino server to 9.0.1 FP10.
If users received SMTP mail, there was a bad encoding characters in message Subject.
The subject looked like this: ?UTF-8?Q?Datov=C3=A9_schr=C3=A1nky:Nov=
The problem was only in the Subject of the email.
I installed IF FP4, but the problem was still the same.
I had to install IF5, which removed the problem.
I upgraded the Domino server to 10.0.1 FP2, , but the problem is still the same.