Bet your iphone has no anti virus and your computer does. That would account for 90% of the "hard" most people see. So lets look at this. * Thunderbird has setting for Gmail. They are stored on the net here. https://autoconfig.thunderbird.net/v1.1/gmail.com * Those settings use oAuth2.0 which is gmails preferred authentication method and ports and encryption that are known to work. However folks often have troubles * Some because their security software and privacy protectors are blocking the process. Interestingly Linux represents a largish proportion of Thunderbird users, but they don't have any where near the same level of trouble as windows users with their anti virus/ Internet security suites do. * Many anti virus products want you to give them access to all your secured connection information and if you do not they barf and refuse to allow communications. Kaspersky is big on the making of them a certifying authority, even though they do not submit their business to the sort of audit certifying authorities must. They are not alone, they just lead the charge. * Third part products that are supposed to make the device more secure that disable cookies. So oAuth which required cookies does not work. * Third part products that assume the probing done by Thunderbird to get the mail settings when the provider is unknown is a hacking attempt to block Thunderbird. A fool idea, but there is no reasoning with multi national security companies. Their bizarre ideas are gospel according to them. (yes symantec I am looking at you) So you tell me exactly nothing about your computer, the error message you receive or the actual providers involved. So I am left to guess around the above list of common failures. I would suggest you try doing it with your anti virus disabled. If you are an ATT customer, that will complicate matters as they have a contract with yahoo to provide broken security.