[ios][Mail][App] no way to change S/MIME signing hash algorithm (from SHA1 to higher SHA256, etc)

Recently I applied a Comodo free email certificate for my AppleID iCloud email address. Then I tried several days to re-create a well-chained p12 keypairs (private key + public/cert key-chain with issue key and CA root key in p7b). Then I installed it on iPhone profile, and assigned iCloud SMTP S/MIME signing identity.

However, send some signed emails from iOS Mail App, all these emails were identified by GMail App and web UI as:

"The signature uses an unsupported algorithm. The digital signature is not valid."

After some experiments to compare sending email from MS Outlook with Trusty E-mail options. I finally find the clues in mail headers, the S/MIME signing header shows:

micalg=SHA1 (by Mail App) and

micalg=SHA1|SHA128|SHA256|... (by Outlook with Trusty hash algorithm varied).

The GMail only considers micalg (hash algorithm) could be valid for those algorithms secured than SHA1. (less collision). I know that for SHA1's setting, it can be most compatible to may old IT infrastructures. But however, for a modern and flexible OS like iOS. Apple should provide more specific option in Settings/General/Profiles/ or Settings/Account/Mail/SMIME/Hash

Or maybe somebody else can suggest another email client on iOS, which can deliver more secured hash algorithm when signing S/MIME signature with certificate.