Using Firmware_Update_Attachment.ino as bootloader

[rtek1000]

Hello, I researched a little more, and it may not be necessary to use another ESP32 to update and ensure the email updater works in case of an update failure or program bug.

There are 2 possibilities that are similar, use a custom bootloader, or use multiple Apps.

Can email updater be part of the bootloader?

So the email updater would never reprogram its own memory region in a typical update.

[mobizt]

The library when it used in firmware update, it utilizes the Updater core library (Update.h or Updater.h) which small decoded base64 chunked data from attachment will be written to flash via Updater.

It depends on you to use this library as part of bootloader, but this library required internet and the IMAP data parser which consumed time and memory.

There are easiest and simpler methods to perform OTA update that are available through the stream interfaces e.g. serial, file, http client and many more.

For OTA update recovery you can read the ESP32 or ESP8266 Arduino core documentation that may be supported.