Msmtp and Broken pipe

Since it seems that ssmtp cannot handle the emails with the
attachments we were sending, I decided to give msmtp a try. So,
I set it up following the wiki at
http://wiki.bestpractical.com/view/msmtp and sent a test email. In
/var/lo/syslog I got:

Nov 17 15:06:08 tickets RT: About to commit scrips for transaction #2323
Nov 17 15:06:08 tickets RT:
rt-3.6.7-3079-1258488364-624.133-5-0@domain.com #133/2323 - Scrip 5
(/usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm:266)
Nov 17 15:06:09 tickets RTmailer: CALL /usr/bin/msmtp -nt -oi -t RETURNED 78
Nov 17 15:06:09 tickets RT:
rt-3.6.7-3079-1258488364-624.133-5-0@domain.comCould not send mail:
Close failed: Broken pipe at
/usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm line 342.
Stack: [/usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm:342]
[/usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm:288]
[/usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm:107]
[/usr/share/request-tracker3.6/lib/RT/ScripAction_Overlay.pm:242]
[/usr/share/request-tracker3.6/lib/RT/Scrip_Overlay.pm:507]
[/usr/share/request-tracker3.6/lib/RT/Scrips_Overlay.pm:195]
[/usr/share/request-tracker3.6/lib/RT/Transaction_Overlay.pm:181]
[/usr/share/request-tracker3.6/lib/RT/Record.pm:1466]
[/usr/share/request-tracker3.6/lib/RT/Ticket_Overlay.pm:2435]
[/usr/share/request-tracker3.6/lib/RT/Ticket_Overlay.pm:2348]
[/usr/share/request-tracker3.6/lib/RT/Interface/Email.pm:780]
[/usr/share/request-tracker3.6/html/REST/1.0/NoAuth/mail-gateway:61]
(/usr/share/request-tracker3.6/lib/RT/Action/Sen
Nov 17 15:06:09 tickets RT:
rt-3.6.7-3079-1258488364-624.133-6-0@domain.com #133/2323 - Scrip 6
(/usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm:266)
Nov 17 15:06:09 tickets RT:
rt-3.6.7-3079-1258488364-624.133-6-0@domain.com No recipients found.
Not sending. (/usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm:278)
Nov 17 15:06:09 tickets RT:
rt-3.6.7-3079-1258488364-624.133-7-0@domain.com #133/2323 - Scrip 7
(/usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm:266)

Why would I be getting a broken pipe?