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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