Under the "SMTP" settings for my project, "custom SMTP" is enabled. I also changed the sender name on the SMTP servers just so I could update it, and appwrite says "SMTP server has been enabled" upon save. Thus, custom SMTP server is enabled within config.
TL;DR
After updating to version 1.4.3, an SMTP error message "SMTP disabled (503)" is appearing when appwrite tries to send an email. Disabling and re-enabling the custom SMTP setting did not resolve the issue. The user also tried changing the sender name on the SMTP servers but the problem still persists. The custom SMTP server is enabled within the configuration.