You have not stated your objection to the Gmail client.  When SM and GMail were incompatible, I did some shopping.  Nine was the only one that just connected my phone to my server, the others put their server in the middle.   I would rather pay for the product than surrender my data and become the product.  The only alternative actually tested was Outllok, which Intercepted my data without disclosure and inserted 10 minutes of delay.   They have probably fixed the delays.  I switched back to Gmail client when SM upgraded their EAS implementation.

I Douglas! 

There's no complains in how Gmail app works.

Simply there'are customers that want completely separate their business email from their personal email.

Stated that almost everyone have a Gmail account in Android, the best solution seems to have a separate app to use with SmarterMail.

Been pretty happy with Nine. A few silly glitches, the most notable is that in parts of the app you are in conversation mode when you wanted that disabled.

Yes it's a paid app, but you only pay once, it's not a subscription model (last I looked).

Hi Paul!

You are right, but I'd like to know if there are also other apps...

If there aren't, lastly I'll go with Nine.

Not lecturing you here, because you probably already know this: I sometimes find that going with something that works, that costs a reasonable amount, saves the hassle of researching other products, and then having to learn how they function.

In many cases, I simply tell my client what the cost is, and they go for it. You might not be so fortunate.

Yeah, you are right!

...but I'm curious to find also other altenratives (if there are...)... ;-)

Still haven't found alternatives to Nine that I like as much. But in my case, my clients are moving to Microsoft 365 en masse. My SM installs are split-domain configs SM <--> M365.

BTW the Outlook smartphone app, on both IOS and Android, AFAICT, has been re-binked to ONLY allow connecting to "real" Microsoft Exchange server or Microsoft 365. Does not work with SM EAS any longer. Not sure if it works with EWS. 

And the advantage of the Outlook app with M365 is that searches traverse the entire server datastore, not just the email that's downloaded to the phone.