Fix SMTP RFC violation for better interoperability

Space after colon violates RFC 5321 (and RFC 821): "Since it has been a common
source of errors, it is worth noting that spaces are not permitted on either
side of the colon following FROM in the MAIL command or TO in the RCPT command"

This was merged in AOSP: https://android-review.googlesource.com/#/c/32640/

Change-Id: Ie5330bf2bd01cd8f734134dadd742cf16df70d7a