Ok I think I understand what is wrong. It seems that the SMTP library used by sourcehut LMTP daemon does not understand [1] the "ORCPT=" part in the RCPT-TO command that seems to be allowed by the RFC1891.
Until aiosmtpd support RFC1891, is there a way that OpenSMTPD can get rid the ORCPT part? [1] https://github.com/aio-libs/aiosmtpd/issues/183
