The standard iOS mail app only supports one signature for all emails, but I'd like an app that supports individual signatures for multiple emails, if possible. Does anyone know of any?
The standard iOS mail does have multiple signatures if you have multiple email accounts on it. I think it's in setting, mail contacts and calendars then sigs.
Im confused are you asking about multiple signatures per single email account?
If you are asking about a different sig per different account then the builtin app handles this quite well
You could also use the Microsoft Outlook app which handles this well as well