Why are there limits to attachment sizes in some places and not others?

Well, first we have to make sure to compare apples to apples – comparing
Hotmail to Thunderbird is really an invalid comparison. I realize that you see
them as “email”, but in fact they are two very, very different things.

And then we need to talk about costs, and speed:

Hotmail’s costs, and your recipient’s speed.

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Hotmail is an email service. When using Hotmail you’re using their servers and their infrastructure not only to send and receive email, but also to store it. They are both an “email service provider” that handles getting email from point A to point B, but they’re also an email “interface” (for lack of a better term) where you can compose, store and read your email, as well as manage contacts and a host of other things.

Gmail, Yahoo mail, and any number of online services are the same. With only a web browser, you have access to both an email management interface, and the infrastructure to get email delivered.

Thunderbird is only the second half of that equation. Thunderbird is a program that you run on your PC that is an email management interface. You can compose, store and manage emails and a contact list and more. It’s a lot like a word processor that way: it’s just a program running on your computer and not a lot more.

If all you have is Thunderbird you don’t have enough to send and receive email.

You must configure Thunderbird to connect to an email service provider – perhaps your ISP, perhaps some other service, or perhaps even Hotmail. Only then will Thunderbird be able to actually send and get email.

Thunderbird doesn’t know how to route your email to its destination. All it knows how to do is to connect to the email service that you configure.

And programs like Outlook, Outlook Express, Eudora, and many others are the same. They’re simply PC email management programs that still need to connect to an email service provider in order to send and receive email.

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It’s the email service providers that impose limits.

Hotmail may have a 10MB attachment limit, another service may have another limit, and yet another service may have no limit at all. Since Thunderbird might be used to connect to any of these services on which you have an account, it’s not going to impose a limit, since it can’t know what those limits might be. Rather, the email service will – if it has a limit – when you attempt to send an email that’s too large.

When you use Hotmail directly through its web interface, you may get notified of the limitation sooner. But even if you connect to Hotmail using Thunderbird (which is quite possible these days) you should also see this same limitation when you attempt to send.

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So why are there limits?

It boils down to two reasons:

• Not everyone has a fast internet connection. That 10 megabyte attachment you want to send? It could clog up someone’s internet connection for over half an hour if they’re on dialup (and while it’s easy to dismiss dialup, there are still a significant number of people in locations where it remains the only viable alternative to connect). Especially with so many other ways to transfer large files, emailing very large attachments simply isn’t necessary.

• Those attachments take up space. When you’re using a desktop email program like Thunderbird, that space is on your hard drive. But when you’re using an email service like Hotmail, that space is on their servers, and costs them money. Given that it’s a free service, limitations like this (as well as a total storage limitation) are to be expected.

Both of those reasons apply to the bulletin board scenarios you mention, though most often it’s the latter one: the owner of the board is simply trying to manage the disk space used by, and the costs perhaps incurred, by the system.

Disk space has certainly gotten cheaper – we’ve certainly seen storage limits grow dramatically in the last few years – but it’s still not free.