We're saying the same thing? I said no, you can't modify FROM, but you don't want to (for my/these purposes anyway).
What you can do, and what the code does (with values from env) is set the envelope addresses.
The email ('letter') inside is still from the original sender, and to my original receiver. It's just 'repackaged' in an 'envelope' from my relay (some arbitrary but SES verified address) to wherever I want it to end up (e.g. Gmail in your case).
It looks like you tried to send 'from' Gmail, which doesn't make sense, [edit: I suppose you could verify just your Gmail address in SES, if you really wanted to use that as the 'envelope from'/`MAIL FROM`] in this setup you want to send it on from Lambda (SES having received it) to Gmail.
What you can do, and what the code does (with values from env) is set the envelope addresses.
The email ('letter') inside is still from the original sender, and to my original receiver. It's just 'repackaged' in an 'envelope' from my relay (some arbitrary but SES verified address) to wherever I want it to end up (e.g. Gmail in your case).
It looks like you tried to send 'from' Gmail, which doesn't make sense, [edit: I suppose you could verify just your Gmail address in SES, if you really wanted to use that as the 'envelope from'/`MAIL FROM`] in this setup you want to send it on from Lambda (SES having received it) to Gmail.
More about email 'envelope's here (just my first search result, looks ok) https://www.mybluelinux.com/what-is-email-envelope-and-email...