from the log it seems that lemmy cannot reach https://midwest.social/ - if you have more such operation timed outs - probably there is some networking issue with outgoing requests - maybe you have some kind of firewall? i can reach your instance from other direction: https://group.lt/c/[email protected]
probably the easiest way to setup lemmy and another front facing reverse proxy is to use nginx that comes with lemmy on another port and setup simple reverse proxying with NPM to it. i myself using caddy for reverse proxying, using this config: https://join-lemmy.org/docs/en/administration/caddy.html
you should be able to use any mail gateway that supports smtp. one way to do it is to configure postfix to use sendgrid as relayhost - https://docs.sendgrid.com/for-developers/sending-email/postfix