[horde] Error adding recipient

[Knowles Burrell]

I have a fresh install of horde to use as a webmail platform. When
trying to send a msg this error is received:

There was an error sending your message: unable to add recipient
[emal at email.com]: Invalid response code received from server

I have searched through the FAQ and tried to search past posts on here
but I have not been able to find any tips for fixing it. Any help to
point to resloving this would be appreciated.

Thank you,
Knowles