We are in the process of going from V5R4 (our old 520 iSeries) to V7R1 (our new shiny E4B iSeries) but sending mail did not work. Getting weird messages in QSYSOPR. After all my ideas were exhausted I was lucky in the last seconds before giving up and handing it over to the IBM guys. It appears that the CHGSMTPA command in V7R1 has some new parameters/keywords, FWDHUBSVR being one of them. Freshly added keywords get a default, in this case *NONE, and that appeared to be the villain.
Giving FWDHUBSVR the same value as MAILROUTER solved all my problems (why this new keyword was introduced/needed and why IBM didn’t gave it the default value of the MAILROUTER value I don’t know, but this problem gave me a real headache for 2 days)
CHGSMTPA MAILROUTER(‘10.100.10.103’) FIREWALL(*YES) FWDHUBSVR(‘10.100.10.103’)
— Max
Encounters with Reality 
Thank you Max! This was the last push that got us successful with sending email from IBM i.
You are welcome:)
Gotta love the Internet, gift from God (Surely ARPA had different plans!)
This great web page also resolved the issue I had fought for weeks in trying to be able to send csv reports out by email. And just in time.
You are most welcome:)