Salesforce

Salesforce can send a person's one-to-one email through their own Microsoft 365 mailbox, and Footer365 signs mail that passes through Microsoft 365. This guide covers Sales Cloud. Choose how your CRM or app sends its mail explains the two ways to send, and this guide follows the first.

At a glance

• Can be signed: email your people send through Salesforce with Send through Gmail or Office 365. Salesforce says: "The emails your reps send through Salesforce come from their Gmail or Office 365 email addresses."
• Cannot be signed: workflow and trigger email, which Salesforce says "are still sent through Salesforce", and Marketing Cloud Engagement email, which Salesforce sends from sending IP addresses of its own.
• How it connects: each person connects their own Microsoft 365 mailbox. The pages Salesforce publishes that could be read do not say whether it uses Microsoft Graph, SMTP or another protocol.
• Status: from Salesforce's documentation as read on 23 October 2026, not tested by Footer365.

Before you start

• Footer365 mail flow is set up. With the Outlook add-in only, no mail Salesforce sends is signed. Using the Outlook add-in only
• Every person who sends from Salesforce has a Footer365 signature rule that covers them.
• Salesforce says people need either the standard user profile or the Send Email through External Email Services user permission. It also says people with an Einstein Activity Capture (EAC) or Inbox licence cannot use the feature: "EAC and Inbox users cannot use Send through External Email Services feature." Salesforce tells them to use their email client, Gmail or Outlook, directly, and Footer365 signs mail written in Outlook like any other.

Step 1: Approve the app in Microsoft 365

The Salesforce pages that could be read do not say which Microsoft permissions Salesforce asks for, or whether an administrator has to approve them. When a person connects their mailbox, Microsoft may show an approval screen, or "Need admin approval". Approve it by one of the three ways in Approve an app's access in Microsoft 365, after reading the permissions on the screen.

Step 2: Choose the mailbox

• Each person's own mailbox is the route Salesforce describes. The mail is signed with the signature your rules give that person.
• A shared mailbox: Salesforce does not document connecting one. Do not assume it works. The wrong signature is used for a shared mailbox or delegate

Step 3: Connect it in Salesforce

1. In Salesforce Setup, enter External Email in the Quick Find box, then select Send through External Email Services.
2. Turn on one of the email services your company uses, here Office 365.
3. Each person then connects their own account. Salesforce says people can customise the name and signature on outgoing email in My Email Settings.

Salesforce's own steps: Send Email Through Salesforce.

Step 4: Check one message

1. Send an email from Salesforce to an address outside your organisation that you can read.
2. Open the headers of the copy you receive.
3. Return-Path should be the sender's own address, and X-Footer365-Relay-Id should be there.
4. Look in the sender's Sent Items. Salesforce's pages do not say whether the message is saved there, so its absence is not a fault by itself.

What other results mean: Mail from our CRM is not signed.

Where the signature goes

Salesforce lets people customise the name and signature on outgoing email in My Email Settings. Its pages do not say how that signature is added to mail sent through Office 365. If people set one, the message may carry two signatures, Salesforce's and Footer365's, so leave it empty if the signature should come from Footer365 alone. To put Footer365's signature where Salesforce's goes, use a marker. Salesforce's pages do not say what Salesforce does with text in double braces, so check one message. Place the signature with a marker

What is not signed

• Workflow and trigger email. Salesforce says: "Emails sent through workflows and triggers are still sent through Salesforce."
• Marketing Cloud Engagement. Salesforce's deliverability training says its customers send from "shared" or dedicated sending IP addresses: "Sharing sending IP(s) with other Marketing Cloud Engagement customers offers a solution". These are Salesforce's addresses, so the mail never passes through your Microsoft 365. Mail that is never signed
• Account Engagement. Not covered: none of the pages read says how it sends. Do not assume it goes through Microsoft 365.
• Delivery information and bounces. Salesforce says: "Bounce management isn't supported when you send through external email accounts." and "Email delivery information for Send through Gmail or Office 365 isn't available in the email logs." Use Microsoft 365's message trace instead.

What stops working

Salesforce's pages do not say that Send through External Email Services depends on Exchange Web Services or on a Basic authentication password. If Salesforce offers a choice of connection when you connect, choose a Microsoft sign-in, never "Exchange" or "EWS". Exchange Web Services is being switched off

Limits

Salesforce's page states no sending limit for this feature. Microsoft's limits for a mailbox apply: 10,000 recipients a day and 30 messages a minute. Microsoft: Exchange Online limits

Last resort: a connector to Exchange Online

Salesforce has a separate feature, Email Relay, that hands mail to a mail server of yours. For Exchange Online it is a dead end. Salesforce says Email Relay "doesn't support sending emails directly through Microsoft 365 Exchange (Exchange Online) to people outside" your organisation, that it "isn't recommended unless you have an on-prem or hybrid solution", and that it can fail with errors such as "Relay Access Denied ATTR36". Microsoft says a connector cannot be used for a service hosted by someone else. Use Send through External Email Services instead. Last resort: a connector to Exchange Online

If it does not work

1. The person cannot connect. Check they have the standard user profile or the permission above, and that they have no EAC or Inbox licence.
2. Microsoft says "Need admin approval". Approve an app's access in Microsoft 365
3. The message has no X-Footer365-Relay-Id. It did not pass through Microsoft 365. It may be a workflow or trigger email.
4. It passed through Footer365 but is unsigned. The signature was not added
5. Still not clear. Mail from our CRM is not signed

Sources

Read on 23 October 2026:

• Salesforce Trailhead: Send Email Through Salesforce, no date shown on the page.
• Salesforce: Email Relay and Microsoft 365, published 15 May 2026.
• Salesforce Trailhead: Set Yourself Up for Successful Deliverability, no date shown on the page.
• Salesforce: Send through External Email Services and EAC or Inbox users, published 17 July 2026.

Salesforce's Setup articles on Send through External Email Services and its considerations could not be read by an automated reader, so this guide states nothing from them.