I'm curious if I can set hudson.tasks.Mailer.UserProperty.UserProperty. MailAddressResolver claims to look for the email as a UserProperty:

So the common technique for a mail address resolution is to define your own {@link UserProperty} types and
add it to {@link User} objects where more context is available. For example, an {@link SCM} implementation
can have a lot more information about a particular user during a check out, so that would be a good place
to capture information as {@link UserProperty}, which then later used by a {@link MailAddressResolver}.

Code changed in jenkins
User: Paul Allen
Path:
src/main/java/org/jenkinsci/plugins/p4/changes/P4ChangeEntry.java
src/main/java/org/jenkinsci/plugins/p4/client/ConnectionHelper.java
http://jenkins-ci.org/commit/p4-plugin/5f936ad0fffc3212a1960b1d7c67c3807c657fe4
Log:
Add Perforce User's email to Jenkins User property.

JENKINS-28421

Code changed in jenkins
User: Paul Allen
Path:
src/main/java/org/jenkinsci/plugins/p4/changes/P4ChangeEntry.java
http://jenkins-ci.org/commit/p4-plugin/e117cd2c9d1a33745191f5c326d4efb0184ace85
Log:
Only set email if User's address in null or empty.

JENKINS-28421

Code changed in jenkins
User: Paul Allen
Path:
src/main/java/org/jenkinsci/plugins/p4/changes/P4ChangeEntry.java
src/main/java/org/jenkinsci/plugins/p4/email/P4AddressResolver.java
src/main/java/org/jenkinsci/plugins/p4/email/P4UserProperty.java
src/main/resources/org/jenkinsci/plugins/p4/email/P4UserProperty/config.jelly
http://jenkins-ci.org/commit/p4-plugin/c1f15ea19c720a3d4840aafa478b177c0d0f8f97
Log:
Created P4UserProperty to store Email address.

P4UserProperty extends UserProperty to store the Perforce User’s email.
Then retrieves it with P4AddressResolver by extending
MailAddressResolver.

JENKINS-28421