Estimate data used by email.
Email itself is tiny — a typical message with headers and HTML formatting is around 75 KB — so message volume alone barely registers against a data plan. Attachments are what make the difference, and because a single 2 MB document outweighs twenty-five plain messages, the attachment share is usually well above 80 percent. That is why the practical lever is switching attachments to cloud links rather than sending fewer emails.
Email traffic split
Text MB per day = emails x KB / 1024; attachment MB per day = attachments x MB each; monthly GB = daily total x 30 / 1024
Yes, initially. An IMAP or Exchange client downloads full messages and attachments for offline access, so the first sync of a large mailbox can be several gigabytes. Webmail fetches only what you open.
Usually repeated full-mailbox resyncs, or attachment prefetching on all folders. Setting the client to sync only recent mail and to fetch attachments on demand typically cuts the figure by most of the difference.
Yes — both cross the connection. Sending a 10 MB attachment consumes upstream data, and if the message goes to five recipients on the same server it is still uploaded only once.