"Blocked sign-in attempt" and "Less secure app" notification
In your Gmail settings under "Account," you can add other email addresses you own so that you can send emails from that account as well as your Google account. If that alias address is also a Google account, Google may reject your sends with a message that looks like this:
You are sending email via me@<mygoogleaccount.com>
You also own me@<othergoogleaccount.com>
You want to set up an alias so that your me@<mygoogleaccount.com> account is able to send email from me@<othergoogleaccount.com>
This message usually is referring to the fact that Google requires you to enter the password for your alias email address as part of the setup process. Google considers outside apps (even their own applications, like Gmail) to be "less secure" if they require knowing your password. If your security settings block "less secure apps", Google will therefore block it's own application from sending the email.
- Update your Google security settings to allow "less secure apps." In many cases organizations have to do this anyway to enable third party apps like Apple Mail.
- Instead of setting up an alias, connect to this Google account directly in Mailshake to add it as it's own sending account.
Screenshot of Google security settings: