Error 500 on GUI when sending mail after update

[AlexP]

After updating to the latest version, I receive an error 500 on the web frontend when trying to send a mail. this happens to all users on that server.
Version in use is: 7.10.6-Rev65

In the logs I found this error message:

java.lang.NoSuchMethodError: com.openexchange.smtp.filler.SMTPMessageFiller.<in it>(Lcom/openexchange/smtp/config/ISMTPProperties;Lcom/openexchange/session/Session;Lcom/openexchange/groupware/contexts/Context;Lcom/openexchange/mail/usersetting/UserSettingMailV
at com.openexchange.smtp.DefaultSMTPTransport.createS MTPMessageFiller(DefaultSMTPTransport.java:142)

Any idea, what's happening there?

Thanks in advance