I have a multi-server setup with separate spamfiltering (eFa) for in- and outbound mailtraffic. This works like a charm using relayhost and native lmtp and smtp host lookup in postfix's main.cf. (Because eFa is in the same internal network I want to use /etc/hosts before dns for host lookup) Code: relayhost = [eFa servername]:25 (setup via ISPConfig) ... some other relayhost related settings lmtp_host_lookup = native smtp_host_lookup = native To catch SPF issues for forwarded emails I've installed PostSRS on my mailservers. PostSRS by itself too works like a charm but has a major negative side effect. The relayhost and host lookup settings are completely ignored. Postfix is doing host lookups in DNS only and relays directly to one of the found MX records. Does anyone have a solution to how to tackle this side effect and make postfix do native host lookups again and relay to the host I've set? It happens on older CentOS 7 servers and newer Ubuntu 20 servers so it's not OS related but purely postfix (version 2 and 3).