I have a perplexing problem. I have an old Samsung Captivate, a Samsung S4, and a Samsung S5. The Capitvate is running on Froyo, I think. The S4 is running on 5.0.1 and the S5 is running on 5.1.1 (to which it just updated this morning from 5.0.1). I have two Gmail/Google accounts. Both Google accounts are running successfully on the Gmail app on all three phones. Until yesterday, both Google accounts were also running successfully on the native Samsung email app on all three phones (I sometimes use the native Samsung email app because I occasionally need to use a larger font size, which isn't available in the newer Gmail apps). All day yesterday, I was using the Samsung email app for both accounts with no issues. Then late yesterday, with the S5 only, before the OS update, using the Samsung email app, I sent a reply from email account #2, and it bounced back saying that a sign-in attempt was prevented due to an app that failed to meet Google's security standards. I resent it, and it bounced again. Curious, I tested sending from email account #1 with the Samsung native app, and got the same result - sign-in attempt was prevented. Now more curious, I tested sending from both accounts on the Samsung native app with my S4, but those went through successfully. Figuring that something was goofed up with the account settings in the native app on the S5, I deleted both native email accounts and proceeded to set them up anew. Account #1 set up successfully and sends and receives as expected. Account #2 fails the setup - I get an "authentication error" message. Meanwhile, both accounts work fine on the Gmail app, and both accounts work fine on the native app and Gmail app on the S4. The account setup parameters on both phones are identical. Nevertheless, I went on line through my computer and checked/double-checked my Google account security settings for both accounts, verified the authenticity of recent log-ins, verified the single-step authentication process. All is OK there. To test further, I installed BlueMail on the S5 and successfully set up the account #2 that wouldn't set up on the native Samsung app. I don't like BlueMail - I just wanted to see if the problem would duplicate in another app - and it didn't duplicate - setup was successful. This morning, the OS updated to 5.1.1, but the setup problem persists. So, the problem seems to be associated only the native Samsung app with this one Google account and only on the S5. Any thoughts or suggestions? Thanks.