~ DISTRIBUTING any type of copyrighted files is ILLEGAL (unless, of course, you have permission to distribute the music from the author or the publisher). ~
Gmail is extremely handy if you want to send mp3 files to friends. It takes a while, but when Gmail is ready sending your mp3 message, it copies a version of your message to your sent items. This way, you can have all your mp3 files online, wherever you go, without any use of electronic equipment.
If you want to subscribe to a service using a Gmail account, you can use the plus addressing technique -- a modified name of your account that you use to keep track of that subscription. As an example, if your account is firstname.lastname@example.org, and you want to subscribe to the newsletter "bestnewsletter", you can use the email@example.com: the emails will still go to your firstname.lastname@example.org account, but looking the "to:" field will you will have email@example.com. This can then be used for a filter, and one can understand who is giving away the account to spammers.
If you store all your messages, you can excess the quota. To avoid this, you can use filter.
For example, you can create a filter with the operators is:starred and label: (i.e. label:saved, if you created the label saved and marked all your important messages with this label) and select Delete it.
You can go to the Trash to read your messages. After reading the message, if it is an important one, you can star it and press the "Move to Inbox" button to save it. Your starred messages are not going to be moved to the Trash again, creating the indicated filter (with the "is:starred label" in the "Doesn´ t have" field).
The emails in the Trash are automatically deleted forever in 30 days.