I use Jenkins email-ext plugin to send emails when a build starts. When I specified only one recipient of such emails, everything worked smoothly - I got emails.
But wh
what worked for me was giving a comma and space between email addresses, such as:
x1@jenkins.com, x2@jenkins.com, x3@jenkins.com
XML representation of the Jenkins job looks as:
... x1@jenkins.com, x2@jenkins.com, x3@jenkins.com false true true
It has been sending mails all good with this.