According to the Free Dictionary, "unsolicited" means that something is not searched for or sought after. Dictionary.com notes that "unsolicited" can mean something is supplied without asking for it.
Wikipedia notes that unsolicited emails in the form of spam are sent to multiple people, and these emails may be scams. Computers viruses may be responsible for excessive spam, and spammers may sell email addresses to other parties. The legality of these emails depends on jurisdiction, but spam is considered legal in the United States.
The Federal Communications Commission mentions unsolicited calls as a problem for many people. In response to these calls, Congress adopted the Telephone Consumer Protection Act in 1991 to protect people from receiving unsolicited calls from telemarketers. Callers must identify who they are and their company affiliation under the rules. They must also comply with the wishes of people who want to be added to the Do-Not-Call registry.