Nutshell

Nutshell connects a Microsoft 365 mailbox with its email sync, and Footer365 signs mail that passes through your Microsoft 365. Nutshell's page is short, so this guide says plainly what it does not cover. 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 sent from Nutshell through a connected Microsoft 365 mailbox, if it passes through Microsoft 365. Nutshell says Office 365 users "can use the 2-way email sync with Nutshell and will not need to establish SMTP settings."
• Cannot be signed: anything Nutshell does not send through your mailbox. The page read does not say how mass email is sent, so check one message.
• How it connects: Nutshell recommends: "If you are using Office 365, we recommend using our email sync to connect instead of SMTP." The page does not say whether the sync uses OAuth or Microsoft Graph.
• Status: from Nutshell's documentation as read on 23 October 2026, not tested by Footer365. The article is dated 4 August 2026.

Before you start

• Footer365 mail flow is set up. With the Outlook add-in only, no mail Nutshell sends is signed. Using the Outlook add-in only
• Every person who sends from Nutshell has a Footer365 signature rule that covers them.

Step 1: Approve the app in Microsoft 365

Nutshell's page does not mention administrator approval or which Microsoft permissions it asks for. If Microsoft shows "Need admin approval", approve it by one of the three ways in Approve an app's access in Microsoft 365. If you use the SMTP option, Authenticated SMTP must be on for the mailbox. Turn on SMTP sign-in for one mailbox

Step 2: Choose the mailbox

• Each person's own mailbox is what the email sync connects. The mail is signed with the signature your rules give that person.
• More than one address: Nutshell says: "You may use SMTP to connect if you need to send email from more than one email address."
• A shared mailbox: Nutshell's page does not mention shared mailboxes. Do not assume it works.

Step 3: Connect it in Nutshell

Nutshell's page gives no Office 365 steps and links to a separate article for connecting email. Follow that article and choose the email sync. If you must use SMTP, Nutshell says "You might find that 'smtp.office365.com' works as the hostname.", and that it requires SSL or TLS, and asks for the primary address in Username and the primary password in Password.

Nutshell's own page: How to send and get emails from inside Nutshell.

Step 4: Check one message

1. Send an email from Nutshell 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. Nutshell's page does not say whether the message is saved there.

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

Where the signature goes

Nutshell's page does not describe a signature setting. If you see two signatures, remove Nutshell's. To place Footer365's signature in a template, use a marker, and check one message, because the page does not say what Nutshell does with text in double braces. Place the signature with a marker

What is not signed

The page read does not cover mass email or anything else Nutshell may send from its own servers. A message without X-Footer365-Relay-Id did not pass through your Microsoft 365.

What stops working

The SMTP option asks for a user name and password. Microsoft has announced that Basic authentication for SMTP is turned off by default for existing organisations at the end of December 2026, and Nutshell's page does not say that its SMTP option signs in with OAuth. Use the email sync instead, as Nutshell recommends. Turn on SMTP sign-in for one mailbox

Limits

Nutshell states no sending volume limit, and says its SMTP connection attempts "are throttled to avoid being automatically blocked by your server." 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

Nutshell's page describes no connector from Nutshell into Exchange Online, and Nutshell runs on its own servers. Microsoft says SMTP relay cannot be used for a service hosted by someone else, and asks such a service for a certificate of your own. So there is no connector route for Nutshell mail. Last resort: a connector to Exchange Online

If it does not work

1. The SMTP connection fails. Nutshell says to wait 5 to 10 minutes before trying again after changing SMTP settings, and to contact your email administrator if Office 365 is not your actual email provider.
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.
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:

• Nutshell: How to send and get emails from inside Nutshell, written 4 August 2026.