Horde not sending mail after last plesk update

[ArthurF]

PLEASE HELP

We have 2 plesk servers with centos 5.6 and horde stopped working last week. Everyone is receiving mail okay but mail is not sending although it appears in the sent mail folder. AtMail is working fine.
We are running Plesk 10.2

Here are the versions of horde and qmail we are using.
psa-horde 3.3.10-cos5.build1011110330.18
psa-qmail 1.03-cos5.build1011110330.18

 

[IgorG]

Any errors in /var/log/psa-horde/psa-horde.log ?

 

[ArthurF]

There is nothing in the log file.

 

[IgorG]

Try to find related error messages in /usr/local/psa/var/log/maillog

 

[ArthurF]

It is a sendmail issue with qmail. It is happening on 2 boxes so it must of been introduced in an update last week. I found this and it resolved the problem for now. Will it come back? I am a realative novice at this.
http://forum.parallels.com/showthread.php?t=111102&highlight=sendmail

I did this command:
# ln -s -f /var/qmail/bin/sendmail /etc/alternatives/mta