To access your Gmail in your smart phone or tablet using the native mail app or Gmail app, and to have it synced across your different devices, IMAP is the best option.
Now, with IMAP I have all the mails in my Inbox, SentMail or Drafts synced in my Linux, Windows, Ipad and phone and also in the Gmail web interface (www.gmail.com) perfectly.
I have been using Thunderbird with POP for years and decided to switch to IMAP finally.
I did not delete my POP accounts in the existing Thunderbird as I thought it has all my previous mails intact in case anything goes wrong.
The steps are listed here,
1. Enabled IMAP for Gmail.
Gmail > GearIcon > Settings > Forwarding and POP/IMAP > Enable IMAP and Save Changes.
by default this will be enabled usually.
All the gmail labels that you created or not (including Inbox, SentMail, Drafts etc) will be shown as folders in your Thunderbird. However, Gmail gives you the option to choose the one’s you want.
2. Selected the labels that I want to be displayed in Thunderbird.
Gmail > GearIcon > Settings > Labels and uncheck the “Show in IMAP” option of the labels that you dont want to show (you can change it anytime so dont worry).
I unchecked, Important, Chats, AllMail, and Spam. I keep all my important mails in Inbox itself so, AllMail is not needed.
I was not possible to convert the existing POP account. The method is to disable/delete the POP account and add a new IMAP account.
3. Disabled the existing account.
Edit > Account settings > Your gmail account > Server settings
Unchecked the below
-Check for new messages at startup
-Check for new messages at ever…
-Automatically download new messages
4. Added the new IMAP account
Account Actions > Add Mail Account > Fill name, email and password > Continue > Create Account.
5. Tweaked the Thunderbird settings.
Account Settings > The newly created IMAP account > Server Settings
Check for new messages at startup – Checked
Check for new messages every 10 minutes – Checked
When I delete a message – Just mark it as deleted
Clean up (“Expunge”) Inbox on Exit – Unchecked
Empty Trash on Exit – Unchecked
(Deleted messages are automatically moved to Trash by Gmail and removed periodically)
Account Settings > The newly created account IMAP account > Copies & Folders
When sending messages, automatically:
Place a copy in – Unchecked
(Sent messages are automatically placed in SentMail folder by Gmail)
Drafts and Templates
Keep message drafts in: Other and selected the [Gmail] > Drafts
(This will make the draft appear in the Drafts folder of Gmail and so synced to every other devices)
Account Settings > The newly created IMAP account > Junk Settings
Enable adaptive junk mail controls – Unchecked
(Gmail already has junk mail filtering)
Account Settings > The newly created IMAP account > Synchronization & Storage
Keep messages for this account… – Checked
(This is required if you want offline access to your mails, Otherwise the mail is not fully downloaded until you click on the mail title)
In Advanced you can uncheck the folders where you dont want the full mail to be downloaded. A good candidate here is the Spam folder.
6. Clicked OK to save and close the account settings.
Thunderbird downloaded all the mails and it took almost an hour. I had about 1.5 GB email data.