Why most bought accounts cannot use plain SMTP
Sellers advertise "SMTP enabled", but the two providers that matter have closed that door. Microsoft switched off basic authentication for SMTP AUTH, IMAP and POP on consumer Outlook.com/Hotmail accounts and on Microsoft 365 tenants — a username and password is simply refused. Google still allows SMTP, but only through a 16-character app password on an account with 2-step verification enabled; the account password itself never works.
That leaves exactly three things to get right, one page each. Do them in order for every mailbox you add.
01 · OAuth consent
One-time Google Cloud client and Microsoft Entra registration, redirect URIs, scopes, consent screens and reconnecting a mailbox that lost its refresh token.
0 mailbox(es) connected over OAuth
02 · App passwords
Gmail, Yahoo, Zoho, iCloud and independent hosts over SMTP/IMAP: enabling 2FA, generating the password and the exact host settings per provider.
0 mailbox(es) on SMTP credentials
03 · Proxy & country pinning
Pin every account to its registered country, keep a sticky exit IP per mailbox and match the sending timezone so logins never look like a takeover.
no site-wide default · 0 pinned
What to check after connecting
Run the doctor on the new mailbox in Accounts. It verifies the exit IP and its stickiness, SMTP and IMAP auth (OAuth mailboxes are tested with a real XOAUTH2 handshake), SPF/DKIM/DMARC, then sends a live message into the pool and reports where it landed. An OAuth mailbox that fails with "no refresh token" simply needs reconnecting — Google only issues one on the first consent.