Using personal email addresses with iCloud on El-Capitan

In Apple mail on Yosemite I was able to add a third party outgoing smtp server and use different reply addresses when I composed mail.

This was very handy for support sites etc that I have been registered with for years as they require you to reply the email you signed up with.

In the account preferences in Mail it was possible to add more than one reply address by separating each with a comma.

This does not seem to be possible in El-Capitan.

Does anyone know why this feature was silently removed, or if there is a workaround.

I'll unfortunately have to ditch iCloud if this is not possible.