I need opinions

[pcmedicjax]

I have run Several windows based web servers and mail servers for years. I am venturing out into the world of linux, Mainly for the cost factor. I am running a Debian 9 server with Bind 9 and Apache 2 I need to run email on this server also. I only have my personal domains and a small site I host for my church.Total of 10 domains and 40 email addresses I am looking for opinions on which mail server I should. I only need incoming, outgoing mail and webmail. calendaring is not necessary. I am not running any ecommerce but I will need to secure the mail. I have been burned in the past.

Thanx in advance for your opinions.

[dilberts_left_nut]

Postfix & Dovecot - excellent docs & plenty of howto’s.
Roundcube for webmail.

[debiman]

I am venturing out into the world of linux, Mainly for the cost factor.

please be aware that Linux works differently.
I don't mean technically (that's obvious), but it's a different paradigm because of its non-commercial nature (*).
shortly: nobody's trying to sell you anything, so some things won't be so "smooth", or "user-friendly".
that doesn't mean you are using buggy software, quite the opposite actually.
in any case, i think you made a good choice with debian stable for a server (so do i).

(*) people have written about this a lot, maybe this is still good: http://linux.oneandoneis2.org/LNW.htm

[kedaha]

I have run Several windows based web servers and mail servers for years. I am venturing out into the world of linux, Mainly for the cost factor. I am running a Debian 9 server with Bind 9 and Apache 2 I need to run email on this server also.

An opinion? Well, the cost factor is certainly important; however, although I've never used a Windows server—and never will—I'm sure systems administrations with such a server is done by means of a user-friendly graphical user interface (or GUI), I think that changing to a Linux server, especially a postfix & dovecot server where the initial configuration is done using the command-line interface (or CLI) will involve quite a high time factor; it took me a very long time to learn to configure my own email server. To quote one mailserver guide:

Building a Linux mailserver from scratch to your own liking is a painful process unless you happen to be one of the few folk who do that day in and day out - there is no way around that fact.[ ...]Unless you know what you are doing the end result will likely be either insecure or otherwise subtly non-functional. Merely not working is perhaps the best of bad outcomes.

Another guide, which I can recommend having used it myself in the past, at workaround.org explains very well what is involved getting a Linux email server up and running.
For a related forum thread, please see jalisco's recent topic