Various different SCM plugins implement MailAddressResolver, some of them have performance issues. It would be nice to find a good way to work around this.
Extract MailAddressResolvers to dedicated plugins
Jenkins hangs for ~1 hour after posting 'Sending Email'
CPU on 100% when sending mail
Build hangs trying to send email if an email address isn't defined in Active Directory
Build hangs during while "Sending email"
Builds hanging right before e-mail notifications are sent out - Mercurial
email-ext hangs for long time