Microsoft SBS 2011 Exchange upgrade path recommendations?

I always go with Dovecot when migrating out of MS products.

Dovecot == Free

Dovecot - has many different long term archival + searching mechanisms...

Is it an easy migration? I am not currently hosting any Unix servers. I wonder if adding a Unix server might make my LAN environment more challenging to manage. also, would you suggest running the new server off of our LAN? are there some advantages to moving our email server to AWS?

One thing you haven't mentioned yet is how much email you have.  I have clients who have been in business for 10 years and have 90 GB Mailboxes... and others with 20 GB mailboxes.  And still others with more than 1TB in mail (not on Exchange-YET).  It all depends how much mail is sent and received and what kind of mail is sent and received.

A number of my customers chose to migrate to exchange 2019 and server 2019 - liking everything on-site and under lock and key, and not at the mercy of Microsoft screwing up again and not being able to process emails etc.

I used the eval version of server 2016 and exchange 2016 as a half-way house and did a migration to them, then removed SBS etc., then upgraded the domain level again and migrated to server 2019 and exchange 2019.

This can therefore be achieved in a live environment, with Mail continuing to flow at all times and minimal disruption as the original domain, user SIDS etc., all remain intact.

All customers remained active throughout the migration.

What would you do? Move to an in-house Exchange 2019 server? Move to cloud based 365? Or go with a different email server software? 

- cheaper to keep email on-premise, Microsoft licensing for 365 far more expensive over time.
- what is your learning curve if you switch to a different platform like Linux or AWS?
- server hardware and disk space is fairly cheap these days
- SSD more expensive but well worth the costs due to nearly zero failure points compared to previous mechanical  drive technology.
- build out a RAID config with SSD drives and you’ll last another 10+ years with your next server, although I don’t recommend waiting so long to upgrade :-)

Additionally, I have one user (the person who signs my paycheck!) who prefers to also keep emails in a gazillional .pst archives, which annoyingly sometimes get corrupted and require repair.

PST files really don’t corrupt often. My thinking is this happens because they are created with an old version of Outlook or are accessed from a mapped drive, which causes corruption. What version of Outlook are you using, what platform are you using to migrate to .PST, and are they saved on a network drive and accessed?

When it comes to large amounts of PSTs I migrate them back into an exchange database (.edb file) and manage them from here. Once you fully commit the logs to the database you can copy it anywhere and you don't need to mount it in an exchange server to search and recover data. There's plenty of 3rd party solutions that do this.
 

I’ve got less than 50 mailboxes.....I’ve been using a third party email archiving software which stores those emails in SQL databases. That archive software is somewhat slow to produce search results, so it really only gets queried when there’s some urgent info needed.  

I've experienced the same with SQL archive solutions. It could easily be your old platform though, are you running it on the SBS2011? If you continue with Microsoft, you can easily create an archive exchange database in your new configuration that runs next to the current exchange database. Easier to manage when it comes to archived email. Put a bit more money into server memory upgrade, dual CPU's, and the SQL option will perform better. 365 also offers an archive solution.

Side note, I can’t imagine archiving email from the 1990’s, it seems more of a liability and expense than anything else. Just my two cents, I don’t understand your data as well as you do. The packrat mentality...maybe work on letting this go is something to ponder. Really outside the scope of this thread and what you’re looking to accomplish but think it’s worth bringing up. It creates unnecessary overhead, costs, and liability. Worse case hardcopy everything past 7 years into an exchange database (.edb file), copy to USB, and store offsite.