email_mirror: Downgrade a couple ZulipEmailForwardErrors.
email_mirror: Downgrade a couple ZulipEmailForwardErrors.

These errors may occur in the course of normal operations, and
shouldn't generate a message in the error logs.

kou/zulip,zulip/zulip,eeshangarg/zulip,andersk/zulip,kou/zulip,zulip/zulip,andersk/zulip,eeshangarg/zulip,eeshangarg/zulip,andersk/zulip,eeshangarg/zulip,andersk/zulip,zulip/zulip,zulip/zulip,rht/zulip,zulip/zulip,rht/zulip,rht/zulip,kou/zulip,kou/zulip,zulip/zulip,rht/zulip,kou/zulip,rht/zulip,rht/zulip,kou/zulip,andersk/zulip,eeshangarg/zulip,eeshangarg/zulip,andersk/zulip,rht/zulip,kou/zulip,andersk/zulip,eeshangarg/zulip,zulip/zulip