Will I Get Spam?
Spam is defined by Google as "Unsolicited 'junk' e-mail sent to large numbers of people to promote products or services. They key term in the definition is unsolicited. If you have agreed to join a mailing list and/or receive offers from a company (or their third parties) when you have entered a competition and they then email you - it is not spam.
For example if you sign up to a free lotto site then the chances are that they will email you daily. They do this to remind you to visit their site to check to see if you've won plus they'll include some advertising features. This is not spam as part of the entry requirement is that you receive their email.
Too many people are quick to accuse companies of spamming despite having previously agreed to join their mailing lists! We once got accused of spamming someone when we sent them a Lucky Winning Email!
Dealing With Your Comping Emails
That said, if you enter lots of competitions then you should expect to receive plenty of email! You'll most certainly get a lot more if you sign up to permission marketing sites as they are happy to sell on your details. If you don't wish to receive emails from a competition promoter then you can (or should be able to) opt out of receiving emails when you enter their prize draw.
Optting out should have no effect on your chances of winning.
To be on the safe side make sure that you check the rules or terms and conditions of entry. Part of your competition entry may include being added to a mailing list or agreeing to receive a one off promotional email or having your details passed on to a competition sponsor.
The best advice we can offer is set up a seperate email account specifically for competitions. Keep an eye on the emails you receive and do watch your spam baskets as sometimes your winning emails can end up in the wrong folder!
And don't forget that you can always unsubscribe from a mailing list once the competition has finished.