A mail app sends through port 465 with SSL/TLS or port 587 with STARTTLS: use the one your provider lists, and try the other if a network blocks it. Port 25 is for mail servers passing mail to each other, and many internet providers block it for apps. Of the 23 providers we list, 15 use 465 and 7 use 587.
Port 465
Sending with TLS from the first byte: the app connects and encrypts before it says anything. For years 465 was used this way without a standard behind it; RFC 8314 made it the standard port for it in 2018, and recommends it over STARTTLS. In a mail app, choose SSL/TLS (sometimes just TLS or SSL) for it.
Port 587
The submission port, from RFC 6409: the app connects in plain text, then asks the server to switch to encryption (STARTTLS) before it signs in. Choose STARTTLS for it. Choosing SSL/TLS on 587, or STARTTLS on 465, fails to connect.
Port 25
SMTP's original port, which mail servers use to pass mail to each other (RFC 5321). Mail apps shouldn't send on it: many internet providers block it to stop spam from infected computers. CenturyLink filters it, and Xfinity's mail servers no longer accept mail apps on it.
Which port providers use
Of the 23 providers we list, each with its own guide:
| Port | Security | Providers |
|---|---|---|
| 465 | SSL/TLS | AOL Mail, AT&T Mail, BT Email, Fastmail, Gmail, GoDaddy Professional Email, Hostinger Email, IONOS Mail, Namecheap Private Email, Optimum Email, Rackspace Email, Verizon email (in AOL Mail), Windstream Email, Yahoo Mail, Zoho Mail |
| 587 | STARTTLS | CenturyLink Email, DreamHost Email, EarthLink Email, GMX, iCloud Mail, mail.com, Xfinity Email |
6 of them also accept the other port; their guides say so. Proton Mail sends through Proton Mail Bridge, on your own Mac. Every provider's settings.
When sending fails
- A network is blocking the port. VPNs, firewalls, and office, school and hotel networks often block mail ports. Try the provider's other port, or another network.
- The security doesn't match the port: SSL/TLS goes with 465, STARTTLS with 587.
- The password is refused. Many providers want an app password in mail apps, not the one you sign in to their website with.
- The server name is wrong. Check it against your provider's help pages, letter for letter.
Sending in LocalInbox
LocalInbox sends over SMTP with SSL/TLS or STARTTLS, set per account in Server settings. When the outgoing server doesn't answer on 465 or 587, its message says a VPN, a firewall, or an office, school or hotel network may be blocking the port, and, for providers that take both, suggests the other one.
Sources
What this page says about the protocols comes from their standards, checked in November 2026. The providers' numbers are counted from our settings guides, each checked against the provider's own help pages, and what it says about LocalInbox comes from the app.
Questions
Should I use 465 or 587?
The one your provider lists first. Both are encrypted once set up correctly; RFC 8314 prefers 465, because the connection is encrypted from the start and can't be tricked into staying plain. If one is blocked where you are, try the other.
Why is port 25 blocked?
Because spam sent from infected home computers went out on it. Many internet providers block it for their customers, and mail apps don't need it: they send on 465 or 587.
Does sending need a password?
Yes. Providers ask for your address and password, or an app password, before they'll send for you. In most mail apps it's the same one you use for IMAP.
What is SMTP?
Simple Mail Transfer Protocol, the standard for sending email: from your mail app to your provider's server, and from server to server until it reaches the recipient's.