Allow inbound email only for a specific Domain for SMTP VS- iRule?

Going out on a limb here, and this is completely untested, but based on the SMTPProxy iRule here:

https://devcentral.f5.com/wiki/iRules.SMTPProxy.ashx

I've made a small modification:

when RULE_INIT {
     user-defined: local mail domain
    set static::mydomain "@mydomain.com"
}
when CLIENT_ACCEPTED {
    set chelo ""
    set cfrom ""
    set crcpt ""    
    TCP::respond "220\r\n"
    log local0. "client accepted"
    TCP::collect
}
when CLIENT_DATA {
    set cdata [TCP::payload]
    if { [ string length $cdata ] <= 0 } {
        return
    }
    if { not ( $cdata contains "\r\n" ) } {
        log local0. "get <$cdata> so far"
        return
    }
    if { $cdata starts_with "HELO" } {
        set chelo [TCP::payload]
        log local0. "get helo <$cdata>"
        TCP::respond "250 OK\r\n"
        TCP::payload replace 0 [string length $chelo] ""
        return
    }
    if { $cdata starts_with "MAIL FROM:" } {
        set cfrom [TCP::payload]
        log local0. "get from <$cfrom>"
        TCP::respond "250 OK\r\n"
        TCP::payload replace 0 [string length $cfrom] ""
        return
    }
    if { $cdata starts_with "RCPT TO:" } {
        set crcpt "$crcpt[TCP::payload]"
        log local0. "get rcpt <$crcpt>"

         code inserted to validate receiver domain
        if { not ( [string tolower $crcpt] contains $static::mydomain ) } {
             rcpt to domain does not match allowed
            reject
        }

        TCP::respond "250 OK\r\n"
        TCP::payload replace 0 [string length [TCP::payload]] ""
        return
    }
    if { $cdata starts_with "DATA" } {
        log local0. "get data <$cdata>"
        TCP::payload replace 0 0 $chelo$cfrom$crcpt
    }
    log local0. "payload [TCP::payload]"
    TCP::release
    TCP::collect
}
when SERVER_CONNECTED {
    log "server connected"
    TCP::collect
}
when SERVER_DATA {
    set sdata [TCP::payload]
    if { $sdata starts_with "220" } {
        log local0. "get data <$sdata>"
        TCP::payload replace 0 [string length $sdata] ""
        return
    }
    if { $sdata contains "\r\n354 " } {
        log local0. "get data <$sdata>"
        TCP::payload replace 0 [string length $sdata] "354\r\n"
    }
    if { [ string length $sdata ] <= 0 } {
        return
    }
    log local0. "payload <[TCP::payload]>"
    TCP::release
    TCP::collect
}
when CLIENT_CLOSED {
    log local0. "client closed"
}

Dear Kevin,

Thank you very much. Do you think following, the smaller version would work to achieve the requirement? I made it before I received this one.

when CLIENT_ACCEPTED {
    set cto ""
    set cdata ""
}   
when CLIENT_DATA {
set cdata [TCP::payload]

    if { [string match -nocase "RCPT TO:*" $cdata] } {
        set cto [TCP::payload]
        set fromaddr [regsub -all \[\\r\\n\\s\] $cto ""]
        set toaddrs [findstr $toaddrs ":" 1]
        set todomain [findstr $toaddrs "@" 1]

   if { [ class match $todomain equals "MailAddrList" ] } {
            log local0. "Email Accept based on the receipeint email address"
        TCP::payload replace 0 0 $cto
        TCP::release
        TCP::collect
        else {
        }
                drop }
}
}

I can't test it, but the logic looks sound.

Thanks Kevin!

could you please share the iRule code which would perform below task.

where i would have two pools.

pool 1 should receive mails which are being sent to @firstdomain.com

pool2 should receive mails which are being sent to @seconddomain.com

could you please share the iRule code which would perform below task.

where i would have two pools, need to forward traffic to either of the pools based on specific domain