The Reply By Email add-on doesn’t actually send out any messages. All the
sending is done by the bbpnns plugin. The SMTP settings in the RBE add-on
are only for testing purposes to make sure that the receiving account
supports plus aliases.
How is your site set up for outgoing messages? Are you using some kind of
SMTP plugin/server or is it the native PHP mailer that comes with the
I’d recommend setting up Mailgun.com as SMTP for mailouts (it’s what I have
for all my sites). You can then check the Mailgun logs to see what happened
to those messages that aren’t reaching their final destination.
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