Email attachments

[Diesel]

When you attach a file to an email, what actually happens? Is the file kept in a temp directory on the server? How come attachment limits are so low?

 

[HJB417]

The file is embedded in the mail message. So if you have a 5mb attachment, depending on the encoding, youll have at least a 5mb email message. Attachment limits are probably used to conserve HD space.

 

[Diesel]

And where is the mail message kept? Details

 

[HJB417]

depends on server implementation =/
from the 2 Ive seen, each folder represents a user account, and the filename of each email is a timestamp, e.x.: 20050517134556.eml

 

[Diesel]

Yeh, similar to what Ive seen. How is the attachment imbedded into the message? Any encryption or compression?

 

[patrick24601]

I thought it was done the same way you see attachments on things in UseNet. It is a Mime block of data with a header and footer. The header specifies the mime type and file name. This is all theory - but it would make sense.

 

[PlausiblyDamp]

Attachments are encoded either as UUENCODE (old method, not as common these days), or as MIME. Both encodings take an 8-bit binary stream and convert it into a valid 7-bit stream as per the relevant RFC (IIRC RFC 822)