BoltMail
If my contacts don't enter their first name what happens to their custom fields?
When you create your custom field you can set up a default value for that custom field. If you choose then not to make the field mandatory, then it will be set as the default if the contact does not enter their own details.

By this I mean, if you set up a custom field 'First Name' and set the default value as 'Friend' then if your contacts do not add their first name it will be saved as 'Friend'.

When you then create your email campaign and enter 'Dear %%First Name%%' then you will always have a name displayed in your email. Either: 'Dear John' or 'Dear Friend'