1. Setting up the mail server is not the issue. It's the ongoing maintenance to ensure close to 100% uptime so you don't lose any mail. Having worked as a sysadmin maintaining linux boxes for several companies, mail server maintenance accounted for the vast majority of the hours we spent working on servers. This doesn't even account for the hardware upkeep to keep RAID sets in good shape, tape backups, etc.
2. There is simply no open source project that offers a UI anywhere close to as good as gmail. Yes, someone could take on that project, but it will be years before they achieve a similarly polished result.
3. Sure you could roll your own filtering that would be more effective than gmail's, for you. Again, this is further work that you have to do whereas gmail "just works".
4. SpamAssassin is one of the great open source projects in my opinion. Combined with ClamAV you can get a really robust solution that works fairly well. However (afaik) it lacks the learning heuristics that gmail's huge body of data can provide to keep even the newest template spam out of your inbox.
This is not to say that I don't agree with some of your points, but in my opinion the OP has a valid perspective, which I suspect many IT people who value their own time will share.
I do value my own time, and I'll say it again – post setup, I really spend no appreciable time keeping my mail server running. My VPS provider handles all hardware issues (with zero downtime in the last two years), backups consist of a nightly cron job and require no manual intervention, and the last time I touched my Postfix configuration was over a year ago.
"Rolling my own filtering" consists of placing a single mailbox_command line in the Postfix configuration file, it hardly qualifies as a time sink. Writing mail filters for procmail takes no more time than doing so in Gmail, the difference is that the former lets you write much more expressive and fine-grained rules.
And yes, SpamAssassin does have a built-in learning Bayesian classifier. Which I previously used to learn from anything that I manually classified as spam, but these days I don't even get any spam to invoke it on. See sa-learn(1) for details.
You are missing a very critical point: either you need to rent a virtual or real server and spend time configuring and maintaining it - or you could try and dare to run your mail server from at home on some linux box which will open a whole can of worms...
So gmail gives you an easy and free alternative and you can just sign up and access mail via web, pop3 and especially IMAP, which made it superior to pretty much every single other webmail when they launched that feature - and I believe that is still true today, most free webmail providers don't give you free IMAP. You are "paying" by giving away your private information but evidently, people prefer it to setting up their own mail servers.
Regarding point #1, I have maintained Linux mail servers both for large shops as a professional sysadmin as well as for myself and small organizations, and each has been a very different experience.
In the large environment, mail server maintenance does take a disproportionate amount of time. But that's because the environment is so complicated: there are several layers of servers, mail is stored on NFS so there are weird locking issues, LDAP is used for user accounts, etc. There are some very bad failure semantics and if we're not careful, we start bouncing mail.
My small setups use exactly the same software (Debian, postfix, dovecot, spamassassin) but the environments are much simpler: one server, no NFS, no LDAP. I use a VPS so I don't have to worry about hardware. Backups are an off-site rsync in cron. Failures rarely happen but when they do the semantics are much nicer: temporary failures so the mail is resent later. My VPS host failed for the first time in 5 years recently, so I couldn't get mail for a few hours, but I didn't lose any mail and didn't have to spend any time on recovery.
I also run other stuff on my VPS, so the monthly cost and recurring maintenance overhead (security updates/backups) is amortized. Adding mail as another service doesn't change these costs.
I'm not sure where you're spending time on maintenance. I set up my current mail server 3.5 years ago (postfix, spamassassin, dovecot, sieve, roundcube) and barely ever touch it -- the only maintenance required is the very rare security update.
I use tarsnap for backups, so no tapes required.
I don't love running my own mail server, but as a hacker, I don't see that any of the alternatives are better.
1. Setting up the mail server is not the issue. It's the ongoing maintenance to ensure close to 100% uptime so you don't lose any mail. Having worked as a sysadmin maintaining linux boxes for several companies, mail server maintenance accounted for the vast majority of the hours we spent working on servers. This doesn't even account for the hardware upkeep to keep RAID sets in good shape, tape backups, etc.
2. There is simply no open source project that offers a UI anywhere close to as good as gmail. Yes, someone could take on that project, but it will be years before they achieve a similarly polished result.
3. Sure you could roll your own filtering that would be more effective than gmail's, for you. Again, this is further work that you have to do whereas gmail "just works".
4. SpamAssassin is one of the great open source projects in my opinion. Combined with ClamAV you can get a really robust solution that works fairly well. However (afaik) it lacks the learning heuristics that gmail's huge body of data can provide to keep even the newest template spam out of your inbox.
This is not to say that I don't agree with some of your points, but in my opinion the OP has a valid perspective, which I suspect many IT people who value their own time will share.