Unable to parse the date

# Describe the bug

Maddy somehow is unable to parse the date. I looked a little bit around in the maddy and golang code and i think the problem is related to a missing sign in front of the timezone. Unfortunately i could find the right layout for the time.Parse for my given date string, to make a pull reqeust.

# Logs

DATA error {"date":"Tue, 26 Jul 2022 17:52:00 0000","modifier":"submission_prepare","msg_id":"6d88b676","reason":"date Tue, 26 Jul 2022 17:52:00 0000 could not be parsed","smtp_code":554,"smtp_enchcode":"0.0.0","smtp_msg":"Malformed Date header"}

* maddy version: 0.6.2