If you suspect you've found a bug in Geary, follow these steps to report it:
Search Geary's Redmine issue tracker to see if someone else has reported the bug.
Don't see your bug listed? Congratulations! You've found a new bug. To create an bug report, create an account on Redmine and create a new issue. Be as specific as you can and describe the steps to reproduce it. Don't forget to include details about your operating system and what version of Geary you're running.
For general inquiries, please join the Geary mailing list.