Sending an email from a specific alias could be memorised on each device or based on context
If you have different aliases, the composer always defaults to your account email.
A fantastic feature would be to memorise the alias you use.
1. per device
2. depending on the context
Example: if you have a professional device and a personal device, the app on each device could memorise the "send from" address instead of defaulting to the account email. The "send from" could also simply default to "last used" on a specific device.
Example2: if the context is inside a folder for a specific alias, the app could be smart enough to detect that "new message" action does not require to scroll through the list of aliases. The app could be smart and pick the "send from" that relates to the current folder / recent action.

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AZ commented
It would be useful if the alias can be auto-selected based on the contact. For example, if I only ever email bob@bob.com using Alias #2, then whenever I type in that recipient, the "From" should automatically change to Alias #2.