If your Gmail Pop3 or IMAP password for Outlook is being rejected from Google, try the following setting in your Google Account to fix this.

Google must have recently made some changes on their ends that are rejecting devices connecting to their Gmail or Google Apps Mail servers.

Anyway, to fix this, you would need to turn on the “Allow less secure apps” under the “My Account–> Sign-in & Security–>Allow less secure apps”. Once turned on, Google will allow devices like Outlook client to connect to their servers.

Also, here’s the Pop3/IMAP settings for Outlook

Incoming Mail (Pop3) Server requires SSL.

pop.gmail.com
Use SSL: Yes
Port: 995

Outgoing Mail (SMTP) Server – requires TLS or SSL:

smtp.gmail.com
Use Authentication: Yes
Port for TLS/STARTTLS: 587
Port for SSL: 465

Server timeouts Greater than 1 minute, we recommend 5
Full Name or Display Name: [your name]
Account Name or User Name: your full email address (including @gmail.com or @your_domain.com)
Email Address: your email address (username@gmail.com or username@your_domain.com)
Password: your Gmail password