Email addresses on a (single) opt-in list are not confirmed. Anybody can submit anybody’s address to the list, and it will be there until it is unsubscribed.
Single opt in means that as soon as a contact completes your subscriber form, they are automatically added to your contact List. No additional confirmation or step is required.
Unlike single opt in, double opt-in requires your contacts to validate their email address before being added to your contact list.
When a new contact completes the form on your web site, an email is immediately sent to the address they provide. This email contains a verification link which the recipient clicks on to confirm
that they own the address.
Once the link has been clicked, that email address is added to your contact list.
On a double opt-in list, all email address must be confirmed before they are added. A request for confirmation is sent to the submitted address and the address owner must take some action to confirm that
she/he is the owner of the email address and the address is working and she/he indeed wants to be added.
Most often, the confirmation action is as simple as replying to the confirmation request or clicking on a link. If the link is not clicked, then the contact is not added. If they later
fill in the form again, they will be sent another verification email.
Opt-In email messages are only sent using the owner of the email address’s permission. But because of the prevalence of online forms and surveys where anyone could enter anyone else’s
email address, they created double opt-in. If you’re ever requested to be added to a contact list and immediately received an email asking you to confirm you’re subscription, that’s
double opt-in. Because double opt-in is a reinforcement that your contact desires to subscribe.
Sending your email marketing campaign to willing contacts means your emails will be less likely to be marked as spam. This will help build your integrity and reputation as an email
marketer.
The type of contact list you select for each client completely depends on your requirements.
Listed below are some of the advantages and disadvantages of using confirmed opt-in forms:
Advantages
1. While it does not eliminate them completely, confirmed opt in reduces the probability of spam complaints, because someone with access to the email account has had to click a link specific to them. The
confirmation process will help to ensure that people are only subscribed with their clear consent.
2. You will have a cleaner contact list because people have to use their real email addresses in order to confirm their subscriptions. This also eliminates misspelled addresses and typos.
3. Potentially more responsive contacts, those who are genuinely interested enough to confirm their subscriptions may also be more inclined to respond to your campaign or newsletter.
Disadvantages
1. You may lose a number of potential contacts because people may not bother to confirm their requests.
2. Potential contacts who genuinely want to receive your newsletter may not understand the confirmation process and fail to click the link.
If you have any further enquiries regarding opt-in or double opt-in subscription forms please do not hesitate to contact our friendly staff here at EmailMarketer.



Thank you for the info
Thank you I wasnt sure what the difference was until I read you blog.