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Signature 365
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Signature 365
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  • Get started
    • Signing up for a Signature 365 account
    • Creating a new Signature 365 subscription
    • How to setup Signature 365
    • Signature 365 system requirements
    • Signature 365 required permissions
    • Applying signatures to users and groups
    • Adding additional teammates to manage Signature 365
    • Using two-factor authentication with a Signature 365 admin account
    • Enabling single sign-on (SSO) for Signature 365 management accounts
    • How to use the Signature 365 migration wizard
    • Migrating to Signature 365 from Email Signature Manager
    • What types of messages are supported
    • Signature 365 SMTP host list and IP whitelist
    • Signature 365 reliability and security
    • Signature 365 product roadmap
    • How to uninstall Signature 365 from your Microsoft 365 tenant
    • User guides
      • Using the Outlook add-in in Outlook Classic
      • Using the Outlook add-in in Outlook on the web and new Outlook
      • Using the Signature 365 Outlook mobile add-in
    • Service information
      • What is the difference between client-side and server-side signatures?
      • Do my emails remain private when using Signature 365?
      • Do you store my Microsoft 365 Global Administrator credentials?
      • Is Signature 365 GDPR and CCPA compliant?
      • Does Signature 365 support DomainKeys Identified Mail (DKIM)?
      • Does Signature 365 support Entra ID Dynamic Groups?
      • What Entra ID data is synced with Signature 365?
      • Signature 365 Entra ID enterprise applications
      • Signature 365 Exchange mailbox support
      • Signature 365 ports and URLs
      • Signature 365 Outlook add-in manifest versions
      • Removing Email Signature Manager following migration to Signature 365
  • Signature 365 Web Portal
    • Signature templates
      • Getting started with the template editor
      • Template editor menu options
      • Using custom fonts in Signature 365
      • Inserting an email address or telephone as a weblink
      • Using folders
      • Template revisions and draft mode
    • Designing templates
      • Using campaigns and disclaimers
    • Signature rules
      • Assigning a signature to an email alias
      • Signatures for additional and shared mailboxes
    • Fields
      • Using fields in Signature 365
      • Using custom fields in Signature 365
    • Managing images
      • What types of images are supported
    • Folder Permissions
      • Using folder permissions in Signature 365
    • Integration
      • Updating users & groups imported to Signature 365 from Microsoft 365
      • How to register an additional Signature 365 tenant
      • Configuring your Signature 365 Tenant to use hotlinked images
      • Using hotlinked vs embedded images in Outlook
      • Enabling vCards on your Signature 365 tenant
      • Microsoft 365
        • How to enable Sent Items update
        • Inspecting users and groups configured to use server-side injection
        • Moving Signature 365 to a new Microsoft 365 tenant
        • Restrict access to Signature 365 server-side signatures using an Office 365 Security group
        • Setting a Custom Attribute in Exchange Online for use in Signature 365
      • On Premise
        • Active Directory Connector release notes
        • Database Connector release notes
        • Exchange Agent release notes
        • How to install the Database Connector
        • How to install the Exchange Agent
        • Installing the Signature 365 AD Connector
        • Using the Signature 365 Database Connector
    • Troubleshooting
      • Import Active Directory attributes into Signature 365
      • How to update the Sender Policy Framework (SPF) record
      • Managing multiple tenants from the Signature 365 portal
      • Role-based access control in Signature 365
      • Signature 365 domain shows as "Incomplete setup" within Microsoft 365 Admin center
      • Multi-factor recovery process
      • Outlook add-in reports "The request has failed...."
  • Client-side signatures
    • Deployment and configuration
      • How Outlook client-side signatures work
      • How to install the Outlook add-in
      • How to install the Outlook (Classic) agent
      • Updating the Signature 365 Outlook add-in
      • Enable legacy Exchange Online tokens
      • How to enable debug log in Outlook add-in
      • Managing Outlook's default signature options with the Signature 365 Outlook add-in
      • Managing personal signatures, fonts and stationery for "New" Outlook and Outlook on the web
      • Managing personal signatures, fonts and stationery for Outlook Classic desktop
      • How to set Outlook default fonts for all users
      • Version requirements for the Outlook mobile add-in
    • Troubleshooting
      • Current versions of Signature 365 software
      • Supported Outlook versions for Signature 365 client signatures
      • Nested app authentication (NAA) and deprecation of Exchange legacy tokens
      • Outlook add-in is not being deployed to users as expected
      • Outlook add-in is not adding default signatures to email
      • How to enable remote logging in the Outlook add-in
      • Outlook add-in: Opening the Outlook devtools debug window
      • Creating a security group using dynamic group membership
      • Disabling Outlook signatures in New Outlook and OWA
      • Existing outlook email templates insert signature above email body
      • HTML tags are shown for weblinks and images
      • Outlook Classic inserts a ? instead of the correct character when adding a Signature 365 signature
      • Outlook Desktop - Images appear as attachments when email is saved as draft
      • Signature 365 agent authentication script error
      • Signature 365 Classic Agent cannot support Microsoft One Outlook
      • Signature 365 Outlook add-in is removed after log out
      • Signature images appear as attachments in web mail services
      • Using S/MIME with Outlook mobile
      • Using the Aptos font in Signature 365
      • Using the Outlook mobile add-in in GCC environments
  • Server-side signatures
    • Deployment and configuration
      • How Microsoft 365 server-side signatures work
      • Using Server-side injection to specify the location of an inserted signature
      • Inserting a signature in a specific location with Server-side injection
      • Create an exclusion group to exclude users from server-side injection
      • How to update the group assigned for server-side injection
      • Exclude autoreplies from signature insertion
      • Exclude signatures on Microsoft Planner comment emails
      • Tasks, contacts and voting buttons are removed from internal emails sent using Signature 365 server-side signatures
      • Using Signature 365 with read only access to Microsoft 365
      • How to use Signature 365 together with third-party security solutions
      • How to trial Signature 365 when already using another signature service
      • Using Outlook message recall with Signature 365
      • Recreating the Signature 365 Exchange connectors
    • Troubleshooting
      • Enabling server-side injection in Signature 365
      • A signature is not applied to emails with large attachments
      • Unable to contact the Signature 365 service when using the Add-in with an on-premise mailbox
      • Non-delivery report errors and solutions
      • Non-delivery report 550 5.1.8 Access denied, bad outbound sender
      • Non-delivery report 550 5.4.1 Recipient address rejected: Access denied
      • Non-delivery report 550 5.7.1 Unable to relay this email
      • Non-delivery report 552 5.3.4 Header size exceeds fixed maximum size
      • Server-side injection - Digital Guardian Agent X-dg headers cause 552 5.3.4 error
      • Signature 365 transport agent debug log file
      • Removing the Signature 365 Mailflow rule and Exchange Connectors
  • Frequently asked questions
    • Outlook (Classic) agent release notes
    • Using Signature 365 in a hybrid configuration with on-premise Exchange mailboxes
    • Using Sent Items update does not work when sending on behalf of another user
    • Apple Mail application replaces images with when replying
    • Using a group policy object to disable signatures in Microsoft Outlook
    • How to capture a HAR log from Microsoft Edge DevTools
  1. Signature 365
  2. Signature 365 Web Portal

Managing images

Browse Signature 365 Web Portal guides for supported signature image formats and image handling.

What types of images are supported

Check which image formats Signature 365 supports and the recommended resolution and colour settings for best email rendering.

Using hotlinked vs embedded images in Outlook

Compare hotlinked and embedded images in Outlook, including benefits, drawbacks, and common rendering issues.

What types of images are supported

Check which image formats Signature 365 supports and the recommended resolution and colour settings for best email rendering.

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