Thanks! I am now doing it like this

cat test.msg | /usr/libexec/dovecot/lmtp

[@~]# cat test.msg MAIL FROM:<root> RCPT TO:<test> DATA Subject: AAA subject 977

This is the message 977 body

.

-----Original Message----- Subject: Re: How to send a test message directly to lmtp, to test proxying

On 12.11.2019 15.26, Marc Roos via dovecot wrote:

How to send a test message directly to lmtp, to test proxying?

Using LMTP protocol:

LHLO localhost

MAIL FROM:<me>

RCPT TO:<you>

DATA

...

.

Aki