Develop Branch email problem

almostcompletely

I seem to be having trouble sending email (using the forms plugin module) using a fresh pull from the develop branch today.

My email config contains:
$config['protocol'] = 'sendmail';
$config['mailpath'] = '/usr/bin/msmtp -C /etc/msmtprc -t';

... my server is using "msmtp" as a sendmail replacement.

My error is:
Exit status code: 64
Unable to open a socket to Sendmail. Please check settings.
Unable to send email using PHP Sendmail. Your server might not be configured to send mail using this method.

I'm confused because
1. The service works fine from the server terminal
2. Other vanilla CodeIgniter applications do not have a problem (v2.2.1)
3. Fuel installs using the current stable release work fine
4. An old (maybe 3-4 weeks) git pull from develop branch works fine.

Any ideas?

Cheers

almostcompletely

CodeIgniter's SMTP works fine (assuming the service uses plain text passwords - the usual TLS CodeIgniter bug)...