Issues created/commented on via email often have too much whitespace - double spaces between lines, etc. This makes the resulting descriptions/comments hard to read.

One solution would be to allow the user to specify two new parameters on the 'createissue' and 'createorcommentissue' handlers. These would be as follows:
regex = regular expression to match with in replaceall
regexreplace = what to replace every found instance of 'regex'

I have made these changes to my version of 3.12.3 code and attached the modified files. Three files were modified:

com.atlassian.jira.service.util.handler.CreateOrCommentHandler
com.atlassian.jira.service.util.handler.CreateIssueHandler
com.atlassian.jira.service.util.handler.FullCommentHandler