Problem with Sendmail on first registartion (parameters ?)

I have installed and configured MailPress for the first time. When entering user details in the widget for the first time, no e-mail is sent. Here is a portion of the log :

2011-08-10 22:54:58 000000 — MAILPRESS [NOTICE] – Image found : wp-content/themes/weaver/images/headers/wheat.jpg
2011-08-10 22:54:58 000000 — MAILPRESS [NOTICE] – Image found : wp-content/plugins/mailpress/mp-content/themes/twentyten/images/mailpress.png
2011-08-10 22:54:59 000000 — MAILPRESS [NOTICE] – Disconnecting from makulumutis (MP_Mail)
2011-08-10 22:54:59 000000 — MAILPRESS [NOTICE] – Disconnected (MP_Mail)
2011-08-10 22:54:59 000000 — SWIFTMAILER [ERROR] – There was a problem sending with SENDMAIL :

Expected response code 220 but got code “”, with message “”