Am 26.10.20 um 11:24 schrieb R. Diez:
Hello R, I only wrote about the incoming side - of course, you also want to send mail to remote users, and that includes users with an address of …@myisp.com. They will go to the ISP and be fetched to local from there.
That is not what I had in mind. My users will not go to the ISP and fetch their e-mails from there. They will always go to my internal mail server. If a user is on the road, he/she will connect with OpenVPN first.
Probably I could have said that better: fetchmail will fetch those mails from the ISP, same as any other mails to someone@your.site - the Inbox at your ISPs will always be empty, your users will only interact with the dovecot instance on premise. There is some inefficiency, the price for a simpler setup.
I have seen Microsoft Exchange setups that carried on working locally if the Internet connection was down. If Microsoft can do that, I want to have it too. 8-)
With some tinkering, you can configure your local relay smtp to deliver those locally,
To be more clear - if you have a local smtpd too (not just dovecot and fetchmail, postfix perhaps), that sits between your users MUA and your ISPs smtpd, you can make it recognise someone@your.site as a "local" account and have those mails delivered locally. You have to set up some mappings though, that replicate the ones in your fetchmailrc.
Start of a HOWTO:
- Install dovecot, create virtual accounts for all of your users
- Install fetchmail, make it pull the ISPs IMAP and deliver locally
- Install postfix as a smart relay and deliver locally to locals
Feel free to fill in the details ;)
-- peter