If you use “less secure apps or devices” accessing your Gmail account, you may not be able to do so.
Google lists some examples of apps that do not support the latest security standards include:
- The Mail app on your iPhone or iPad with version 6 or below
- The Mail app on your Windows phone preceding the 8.1 release
- Some Desktop mail clients like Microsoft Outlook and Mozilla Thunderbird.
Google recommends Installing a more secure app that uses stronger security measures such as Gmail. Alternatively, you may change your settings to allow less secure apps into your account, which Google doesn’t recommend this option because it can make it easier for someone to break into your account. To allow less secure apps, please follow this post: How to Allow less secure apps in Gmail