We've been running an internal email system that is built into the
ClearOS operating system (a version of CentOS that functions as a
SAMBA 3 domain controller) for many years. Along with the ClearOS
SMTP/POP server, we've been running MailMan on the same machine to
provide an internal listserv capability. Unfortunately, I'm going to
have to discard ClearOS and go with a Windows AD domain server. I
want to preserve the internal email and listserve functionality, and
I want to run it on one of my new Linux Synology NAS clones.
There are a bazillion options for replacements and I don't have any
reliable basis on which to evaluate them.
Do any of you have recommendations for Linux SMTP/POP server software
that would be suitable for running an internal email system?
By "suitable for running an internal email system" I mean:
1. The system will not/cannot/must not communicate with, or be seen
from, the internet.
The ClearOS SMTP/POP server is configured to only accept, and send,
email within its own domain (though this may be achieved by tweaking
Linux ports rather than directly within the email server, given the
information provided in the next paragraph, I don't know). The host
machine is behind a NATing router that does not have any open ports
for email. I need an email server that can be configured in the same way.
Related to this, I would prefer the ability to configure how the SMTP
server responds to invalid input, including messages addressed to the
internet or to invalid internal addresses. The ClearOS server tries
to send these several times, at increasingly long intervals, so that
it takes 3 or more days to put out a bounce-back message, and this
configuration can't be changed. I would rather that bounce-backs take
place immediately.
2. Must provide all standard POP3 functionality (thank you, but I am
not looking for an explanation of why I should use IMAP instead),
including the ability to communicate with a fat Windows email client
that will sometimes tell it to retain email on the server for a period of time.
3. Free as in beer, preferably, but if not an option, then I would be
willing to pay a reasonable one-time license fee, not based on the
number of email accounts, for perpetual use. I am not willing to pay
for a "software as service" arrangement.
4. Because it is an internal server with no connection to the
internet, it does not have to have all of the high-paranoia-level
security features that an internet email server needs. I will cope
with it if it does not pemit plain text authentication, but plain
text authentication is perfectly adequate and completely safe for my purposes.
5. It doesn't have to have any built-in spam filtering.
The current CentOS SMTP/POP server has annoying spam filtering
features that are buggy and can't be turned off. For example, zip
file attachments (and sometimes docx and xlsx attachments, which are
just zip files) go missing, and it can choke on other unusual file
attachments. None of this nonsense is necessary and I would prefer
for nothing to be built-in that filters spam or messes with
attachments. If any such thing is built-in, it needs to be able to be
turned off, and stay off.
6. If it doesn't integrate true listserv capabilities (no fudging
with "aliases" or numerically-limited forwarding lists) like those of
MailMan, then it needs to be compatible with MailMan.
7. Traffic requirements: I don't know much about what sort of
resources a Linux SMTP/POP server requires. Currently we have about
120 email accounts, each with a 1 GB mailbox on the server, and the
NAS will accommodate that without even blinking. Conceivably someday
we could be looking at more like 250 accounts. To the extent to which
that affects speed/responsiveness, then that's a consideration.
8. Easy to set up and configure, and if not, then EXTREMELY well- and
reliably-documented.
9. <rant>Probably not an option, but, since I want an integrated
SMTP/POP server, then, for the sake of the Mother of All that is
Good, would it be too much to ask for an integrated validation system
in which, just for laughs, the SMTP server simply compares the
sender's address to the POP server's list of valid accounts for that
domain to determine whether or not to accept and relay an incoming
message, instead of performing bollocks-oriented "test sends" back to
the user that will fail if the user's inbox, the state of which bears
no rational relationship to the person's authorization, ability, or
need, to use the SMTP server to SEND email, is full, and calling it
"validation", which it is, emphatically, NOT?</rant>
Thanks for all of your suggestions and the benefit of your experience.
Ken Dibble
www.stic-cil.org
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