This could well be one of those questions that cannot be answered.
Or you'll just tell me to "watch and see" but I'll give it a go anyway.

I have a reseller account.
As a way of helping some friends and "friends of friends" out I've created a "E-Mail" only package.
Very low storage space and I'm hoping low bandwidth limits.
This way people who buy domains purely for a "e-mail address for life" reason can have POP & SMTP access.
I've charged them a nominal £5 a year as I'm hoping it takes up very little resources and that of course helps me pay my fees.
This has all been done on a casual basis, they don't really expect any QOS from me and I just give them a few extra features over what a domain registration/parking company would give them.

Anyway I'm trying to work out what kind of bandwidth an "average" e-mail only acocunt is likely to use.
I've given them 10MB of space and explained e-mail shouldn't be stored on the server, so it gives them space to recieve the odd large attachment.
I'm thinking 100MB of bandwidth really should be enough for anybody.
Does this sound about right to you guys?

Thanks.

Based on our experience, if there is such a beast as an "average" user, they send about 200kb of mail per month and receive a similar amount. Many do much more (one user does over 600MB a month, but that includes a lot of large attachments) and some do much less.

100MB a month is more than adequate for, I'd say, 99% of people... but that's going only from our customers, who may not be a representative cross-sampling. :)

I think 100 mb is good just a question though what about spammers? Do you think it would bring more spammers to your service?

you can also have more plans for emails also not just one plan like you can have a 50 mb, 100 mb, 150 mb, 200 mb or what ever :)

I've had only a single spammer in the last year (who was terminated within four hours...), so my experience is that email hosting isn't something that attracts spammers, but YMMV. From what I can tell they'd rather get dialup accounts and abuse ISP's mail servers...

I've never really worried about the bandwith email customers use. If someone uses a really extraordinary amount (more than a gig, consistently) I politely encourage them to "upgrade" to a higher-priced plan, and the high-traffic business customers are paying set fees for a set quantity of bandwith in GB's. Even high-volume eBay sellers don't generate or get as much email, size-wise, as might be expected. Ok, 100 messages a day might seem a lot, but if they're only 10kb each... One of the reasons I don't limit email bandwith for individuals is because it is, to a certain extent, out of the customer's influence. What do you do if someone buys the cheapest possible email plan with 50mb of bandwith, and then their son starts emailing them photos and movies of their new grandkid?

what I ment by diffrent plans was mabey they want to start out smaller plan (not pay as much not as much usage) then while they use it more they can upgrade to a bigger plan if they choose to.

...and my point, though very badly made, was that "one size sort of almost fits all".

I think fewer people know what volume of email they send/receive per month than know how much space and bandwith their websites need, and we all know what the latter is like. :)

I know I couldn't, with a straight face, charge people differing prices for 50, 100, and 150 megabytes of bandwith... 0.5, 1, and 1.5 GB, sure, but... It comes too close to that oft-debated issue of lowball pricing; at $2 per GB, 50MB is, what, $0.10? Triple that for a profit margin, multiply by twelve, round up, and you're still going to lose so much to merchant/credit card fees... Plus I wouldn't want to take the admittedly real, if slim, risk of getting a spammer for less than $0.50 per month, though.

Maybe it's a good idea from a marketing idea, I really don't know.

Oh I'm not in the hosting business at all.
Although I do own a reseller account it is purely a nice and simple way of keeping all of my domains together and hosted in the one place.
A few people at work have purchased their own co.uk domains after seeing how cheap and easy it is to do and of course the majority of registration companies offer free mail and web forwarding but don't offer POP/SMTP access.
A couple of them use ISP's for internet access that actually stop any e-mail that has the wrong "from" address sent, so in effect they can't actually use the mail forwarding options.

So I step in, create a really low use account and get them to point their nameservers where I do.
Tell them how to use their new account and in return each of them have in effect given me "beer money".
I wouldn't have thought any of them were spamers in disguise, but it is staying at a "friends & family" level, I'm not really opening this service to the world - unless of course I find there is a niche market for such a service in which case I'll consider rolling it out to the masses and then I'll have to watch for the spammers.

Thanks for all the answers btw.