I have recetly encountered a problem with Responsys putting a 2MB cap on the file size we are able to send within an email. It is unlikely that we would ever send a GIF over 2MB but I was keen to do some testing to get an idea of email download times for various file sizes.

On contacting Responsys I was told that anything over 2MB can cause "deliverability issues" with the ISPs and have a "other detrimental effects". The explanation was quite vague and I have been unable to find anything to confirm this online.

Over the last couple of years I have seen a lot of emails with GIFs up to 5MB and even higher. Some of these emails have come from very large multi-national companies. So I am interested to find out why they would be sending these very large emails if it could potentially cause problems with ISPs.

Has anyone got any experience / knowledge on the subject?

Thank you,