Spam is horrible, but filtering seems to work well enough these days. (Which makes me wonder why people are still spamming, but that's a separate post about game theory.)
Filtering doesn't work well enough at all. The fact that you can't be sure if your email was received is a problem. Many companies have over-aggressive spam filters and the recipients sometimes never even see the emails in their spam box - they're either bounced or black-holed. Often this is done by blacklisting IP addresses. When that IP happens to be the mail server of a service provider with many customers, when one of them sends spam, all of them get their emails blocked.
Unreliable delivery is perhaps on of the biggest problems with email. Largely due to faulty spam filtering.
Spam is horrible, but filtering seems to work well enough these days. (Which makes me wonder why people are still spamming, but that's a separate post about game theory.)