Pro-Tip: If you are running SmarterMail on Windows Server 2019 and have HTTP/2 enabled in IIS be sure to have at least one IIS binding for SmarterMail that has HTTP/2 disabled!

The SmarterMail webmail screams on HTTP/2. There is definitely a significant performance increase. However, HTTP/2 is *VERY* unforgiving of slow, high latency, noisy, or lossy connections and will result in a spinning loading icon after sign-in. We have experienced a significant number of users who exhibit this problem and each and every one of them was using Wireless 2G, Wireless 802.11 a/b/g, Satellite Internet, 65Kbs ADSL or in one case AOL Dial-Up, and we even had a user with > 60% Packet Loss. Giving them an alternate URI that uses HTTP/1.1 instead resolved their SmarterMail login issues immediately.

In a ideal world HTTP/2 should be preferred, but you may oftentimes have users who have less than ideal connections who still need HTTP/1.1. Always have a backup plan and have at least one IIS binding with HTTP/2 disabled. You'll be glad you do.