Outgoing versus incoming
A mail client holds two independent configurations. Sending runs through the outgoing block over SMTP, while retrieval runs through a separate incoming block over IMAP or POP3.
They frequently belong to the same provider and are never the same host. A client configured with only the outgoing block sends successfully while showing an empty inbox, which is the usual symptom when half a configuration was copied.
Sending and retrieval are separate protocols by design. SMTP has no concept of a mailbox, folders, or read state, so nothing about the outgoing server tells you anything about where received mail lives.
Required configuration fields
Five fields complete an outgoing configuration.
The server name is the provider's published SMTP hostname, and hosting providers publish their own pairs the same way, Hostinger and Rackspace included. Use the name rather than an IP address, because providers move infrastructure behind it.
The port is 587 for a STARTTLS upgrade, specified in RFC 3207, or 465 for implicit TLS, reinstated as a recommended submission port by RFC 8314.
The encryption mode pairs with the port and must match it. Selecting SSL on 587, or STARTTLS on 465, produces a connection that hangs rather than returning a clear error, and that mismatch is the most common fault on this setting.
The username is normally the full email address including the domain. A local part alone is rejected by most providers.
The password is increasingly not the account password. Providers with two-step verification issue application-specific passwords for mail clients, and Microsoft is retiring basic authentication for client submission in favour of OAuth.
Authentication is not optional
Every modern submission server requires authentication before it will relay. A server that accepts and forwards mail from anyone is an open relay, which is the configuration that made large-scale spam viable and which gets a host blocklisted quickly. We hold our own infrastructure to that bar: Nitrosend's relay host sends no marketing campaigns and is not an open relay, and we stated both in writing to AWS Trust and Safety when they reviewed its reverse DNS in July 2026.
Authentication also has to happen after encryption. A client issuing AUTH before completing STARTTLS on port 587 is refused, and the resulting error usually reads as a credential problem rather than a sequencing one.
Common provider values
Gmail and Google Workspace use smtp.gmail.com on 587 with STARTTLS or 465 with implicit TLS, requiring an app password where two-step verification is enabled.
Those Google values cover more senders than any other pair on this page, and we know because we measured our own base. George, our CEO, pulled all 443 brands (439 users) from our production database and scanned the 252 with a resolvable website, 233 fully, homepage and pricing probe plus DNS MX and SPF. 78% of our users live in a Google mailbox, 52% plain gmail.com signups plus 110 custom domains on Workspace MX, while Microsoft 365 sits near 5%.
Microsoft 365 uses smtp.office365.com on 587 with STARTTLS at TLS 1.3 or 1.2, per the device and application guide. Port 465 is not supported on that path, and SMTP AUTH must be enabled per mailbox.
Consumer Outlook.com and Hotmail use smtp-mail.outlook.com on 587 with STARTTLS.
When this field is the wrong tool
Configuring an outgoing server points a client at one mailbox, which is correct for a person sending their own mail.
An application sending on behalf of a product hits three limits that no server setting resolves. Per-mailbox rate caps sized for a person, a sending identity that is an individual rather than a domain you manage, and no delivery events, bounce classification or suppression state reported back.
A submission service authenticating as a verified sending domain supplies that reporting layer, which is the actual difference rather than any property of the hostname.
It is the rule we give every partner doing client work: sending happens from your own verified domain, verification takes about a minute, never through a personal mailbox account. That is what keeps deliverability strong when the mail is commercial rather than personal.