The pattern is used in info.magnolia.module.mail.templates.MgnlEmail.setFrom(String). If you call e.g. setFrom("Felix Rabe <felix.rabe@magnolia-cms.com>") which is completely valid, it will go down the "else" branch, as the regular expression does not match anything without '"'s or anything with a whitespace before "<".

I propose to shorten the code to just:

    public void setFrom(String _from) {
        try {
            InternetAddress address = new InternetAddress(_from, True);
            this.setFrom(address);
        }
        catch (Exception e) {
            log.error("Could not set from field of email:" + e.getMessage());
        }
    }

and remove the wrong pattern altogether.