If you are using a Gmail , AOL or Yahoo account and trying to send email via the PhoneBurner servers, it is recommended that you set up to use your own custom SMTP server to send via your own email address.
Gmail and Yahoo publish DMARC records telling mail servers not to accept mail from Gmail/Yahoo address when the sending mail server is not actually Gmail/Yahoo. This means that emails often are not received, even in spam, if it is sent via PhoneBurner with a Gmail or yahoo address in the account. AOL does not allow users to send via a third party.
See this page for more information on setting up your own SMTP server.