[FIX] mail.mail: avoid prefetching attachment data in memory while processing mail queue, could fail due to memory limit

Specifically when there are many emails in the queue, prefetching
all their attachments at once when processing the first one
could fail, so not even one mail would be sent.

Added explicit logging when an email triggers a MemoryError,
as well as logging when each email is successfully sent.
[FIX] crm: typo, interrests to interest