If it is something waiting in eM Client to upload to Gmail, then the best option may be to just remove the Gmail account from eM Client, then add it again.
Can I delete just email and then add just the gmail email? Can this be done without loosing Contacts and Calendars on EM Client, I have cleaned these all up on EM Client so do not want to lose them.
The Gmail account is setup as IMAP, so all that is, is similar to webmail. eM Client is just showing you what is on the server. If you remove the IMAP account from eM Client, it does not remove the data from the server. Then when you add the account again, it will resync with the server and everything will be there again.
With Gmail accounts, you can’t just remove the mail and leave the contacts. You will need to remove the whole account, then add it again. The contacts and calendar items are setup the same as email, so all eM Client is doing is showing you what is on the server. Deleting the account from eM Client will not delete your contacts and calendars from the server.
A safe practice is to make a backup using Menu > File > Backup before removing an account from eM Client. Then if anything goes wrong you can just restore the backup.