Let’s say I compose an email with attachments consisting of 1 meg and forward that to ten people. If I send it from Outlook it only has one email in the outbox, so at what point does it ‘split’ into 10?
I guess what I’m really asking is: if I send a 1 meg file to ten people would that add 10 megs to my bandwidth usage, or one?
Strictly speaking, it depends on what our Outlook is connected to and which mail protocol is involved.
Having said that, the odds are Outlook only uses 1 meg of bandwidth to get the mail to whatever is your email server. That machine then spends 10 megs sending it on to 10 destinations. If you are paying by the meg for outbound email service, then you’be spending 10 megs there. But not on the upload/download link between your machine & the mail server.
To further complicate the question - what happens if more than one of the recipients are at the same domain? Appreciate there might not be a single consistent answer to this, but are there mail servers/protocols smart enough to minimise unnecessary duplication?
There are some proprietary servers that can be configured to minimize file duplication for server-side storage. But remember, once those ten recipients download their messages to their personal machines, the server still has to use 10mb of bandwidth to deliver the messages. So you’re really only saving on storage costs.
That said, most mail servers don’t work that way by default; and older MTAs which are designed to deliver messages to things like .mbox files in people’s home directories certainly can’t work that way.