For a large Gmail mailbox, I would prefer a dedicated backup tool instead of relying only on manual IMAP syncing. With thousands of emails, attachments, and older messages, the backup process can become difficult to manage manually.
A tool such as PCDOTS Gmail Backup Tool can be useful for creating a separate copy of Gmail mailbox data for backup and future reference. It provides a more practical approach when you need to handle a large amount of email data without saving messages individually. Before starting the backup, I would also check the available filters and export options to make sure they match your requirements.
If you need to convert EML files to PST for use in Microsoft Outlook, you can use PCDOTS EML to PST Converter. It provides a straightforward way to add EML files or folders and convert them into a PST file without manually moving each email.
The software can process multiple EML files together and keeps important email information such as message content, attachments, sender, recipient, and other details during conversion. This can be useful when you have a large number of EML files and want to move them into Outlook in one go.
