What works offline
You can read data that has already downloaded and remains cached. New messages, server search, sending and missing attachments require a connection. Open important messages and download their files before travelling.
Free disk space without deleting server mail
Storage settings show cache usage and let you limit its size or retention period, or clear selected cached data. This preserves server messages, local drafts, outbox messages, contacts, templates and settings. Some content will need downloading again.
Cache cleanup is not emptying Trash
Clearing the cache removes device copies. Deleting messages or emptying Trash or Spam affects mail on the server and can be irreversible. An app PIN does not encrypt the entire email cache.