Enterprise Business Use Cases
Guaranteed Inbox Placement
Standard PHP SMTP on shared servers is frequently blacklisted by major providers (Gmail, Outlook). The SendGrid API integration ensures your critical “Thank You for Contacting Us” receipts are digitally signed and actually land in the primary inbox.
Massive Concurrency Routing
If your Flex Form goes viral and receives 500 submissions in a single minute, a standard SMTP queue will immediately crash. The SendGrid API handles massive concurrency, effortlessly routing hundreds of administrative notification emails simultaneously without dropping a single one.
Ultra-Detailed, Step-by-Step Setup Guide
Connecting Flex Forms to SendGrid requires generating a highly secure, restricted API Key. Follow these exact instructions to ensure the integration is properly authenticated.1
Step 1: Log into SendGrid
Open your web browser and navigate to the SendGrid login portal. Enter your enterprise credentials to access the main administrative dashboard.
2
Step 2: Access the Settings Menu
Once logged in, look at the left-hand sidebar navigation menu. Scroll down to the bottom of the list and locate the section labeled Settings. Click to expand it.
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Step 3: Navigate to API Keys
In the expanded “Settings” sub-menu, click exactly on the link labeled API Keys. This will take you to the secure credentials center.
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Step 4: Initiate Key Generation
In the top right corner of the API Keys page, click the prominent blue button labeled Create API Key. A configuration screen will slide out or appear in a modal.
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Step 5: Name the Key
In the “API Key Name” field, type exactly:
Flex Forms Production API. Giving it a descriptive name ensures your security team will not accidentally delete it during future audits.6
Step 6: Assign Strict Permissions (Crucial Step)
Under “API Key Permissions”, DO NOT select “Full Access” (this is a massive security risk).Instead, select Restricted Access. A massive list of permissions will appear. Scroll down the list until you find the section explicitly labeled Mail Send. Click on it to expand it, and move the slider to grant Full Access ONLY to the “Mail Send” capability. You do not need to grant any other permissions.
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Step 7: Copy the API Key
Click the Create & View button at the bottom of the screen.SendGrid will generate a very long string of alphanumeric characters starting with Click the token string to copy it to your clipboard.
SG..CRITICAL WARNING: You must copy this token immediately. For security reasons, SendGrid will never display this full token to you again. If you lose it, you must revoke it and start over at Step 4.
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Step 8: Create a Connection (recommended)
Switch to Flex Forms → Integrations → Connections. Create a SendGrid connection, paste the
SG. API key, and connect. For a single shared account you can use Catalog → SendGrid instead.Configuration & Masterclass Usage
Once SendGrid is authenticated and active, it silently takes over the email transport layer for all notifications generated by Flex Forms (such as the “Submitter Receipt” or “Admin Alert” emails configured in the Studio). There is no field mapping required for SendGrid, as it simply acts as the delivery engine for emails formatted by Flex Forms.The Domain Authentication Trap
Strict Sender Validation
If you verified the domain: yourcompany.com in SendGrid's Sender Authentication settings.
You configure a Flex Forms Admin Alert to send FROM: [email protected].
SendGrid intercepts the email payload.
SendGrid sees the FROM domain (anotherdomain.com) DOES NOT match the verified domain.
SendGrid instantly DROPS the email and throws a 403 Forbidden error.
CRITICAL SENDER RULE: To guarantee delivery, the “From Address” configured in your Flex Forms Notification Settings in the Studio MUST exactly match the verified domain you configured in SendGrid (SendGrid Settings > Sender Authentication). If you try to send from an unverified domain, the email will simply disappear into the void.
Troubleshooting & Enterprise FAQs
API Error: 403 Forbidden
API Error: 403 Forbidden
The Problem: The server logs show a
403 Forbidden error when attempting to send.The Solution: You have encountered the Domain Authentication Trap. The “From Address” defined in Flex Forms is not authorized in SendGrid. Either change the From Address in Flex Forms, or log into SendGrid and complete the “Sender Authentication” process for that domain.Configuration Reference
The following advanced settings are available in the Flex Forms UI for this integration. Use this reference to understand exactly how each field impacts the API payload.Global Settings
Located in Integrations in the Flex Forms left rail.password
required
SendGrid API Key
The master API key that allows Flex Forms to send emails via SendGrid’s v3 Mail Send API. Create this in Settings → API Keys. It must have the
mail.send permission scope.text
Default from email
The fallback sender address (e.g.,
[email protected]). CRITICAL: The domain in this email address must be fully authenticated in your SendGrid Sender Authentication settings. SendGrid will silently drop emails sent from unverified domains.text
Default from name
The fallback sender name (e.g.,
Flex Forms System).Form-Level Settings
Located on the form hub Integrations tab for a specific form.Envelope & Addressing
text
required
To
The destination email address. You can provide a hardcoded email (e.g.,
[email protected]) or use a merge tag to dynamically send the email to the respondent (e.g., {{email_input}}). Separate multiple addresses with commas.text
From email
Overrides the Global Default From Email for this specific form. Must still belong to a verified SendGrid domain.
text
From name
Overrides the Global Default From Name.
text
Reply-To
When the recipient clicks “Reply” in their email client, their response will go here. Highly recommended: Set this to the user’s email block (e.g.,
{{email_input}}) so your team can reply directly to the submitter.text
CC
Carbon Copy addresses. Comma-separated.
text
BCC
Blind Carbon Copy addresses. Comma-separated. Excellent for silent auditing.
Email Content
text
required
Subject
The subject line of the email. Supports merge tags (e.g.,
New Lead: {{company_name}}).textarea
required
Message body
The actual content of the email. You have full control over the layout. Use merge tags to inject form answers.
select
default:"text/plain"
Content type
Determines how SendGrid parses your
body.Options:text/plain: Standard, unformatted text. Safe and reliable.text/html: Allows you to write raw HTML in thebody(e.g.,<h1>New Lead</h1>). SendGrid will automatically generate a plain-text fallback version for older clients.
Attachments
text
Attachment fields
If your form contains File Upload blocks, type their exact names here (comma-separated). Flex Forms will automatically extract the files from the submission, Base64 encode them, and inject them directly into the SendGrid JSON payload as native email attachments.