Audience
Web developers building applications that send transactional or automated emails and need a local tool to test, debug, and validate those emails before deployment
About HELO
HELO is a desktop application designed to simplify email testing and debugging for web developers by capturing and analyzing outgoing emails generated by applications during development. Instead of sending emails to real recipients, HELO exposes a local SMTP server that intercepts outgoing messages and displays them inside the application, allowing developers to inspect and verify them before deployment. This approach helps prevent common problems such as broken links, missing images, formatting errors, and other issues that often appear in production emails. It provides detailed debug views that show the email in multiple formats, including HTML rendering, plain text, raw source code, and full message headers, giving developers a complete understanding of how the message is structured. Automated validation tools check links within the email to confirm they return valid HTTP responses, reducing the risk of sending emails with invalid or broken URLs.
Other Popular Alternatives & Related Software
MailHog
Inspired by MailCatcher, easier to install. MailHog is an email testing tool for developers: Configure your application to use MailHog for SMTP delivery. View messages in the web UI, or retrieve them with the JSON API. Optionally release messages to real SMTP servers for delivery. See MailHog libraries for a list of MailHog client libraries. ESMTP server implementing RFC5321. Support for SMTP AUTH (RFC4954) and PIPELINING (RFC2920). Web interface to view messages (plain text, HTML or source). Supports RFC2047 encoded headers. Real-time updates using EventSource. Release messages to real SMTP servers. Chaos Monkey for failure testing. See Introduction to Jim for more information. HTTP API to list, retrieve and delete messages. See APIv1 and APIv2 documentation for more information. HTTP basic authentication for MailHog UI and API. Multipart MIME support. Download individual MIME parts. In-memory message storage. MongoDB and file-based storage for message persistence.
Learn more about MailHog
GlockApps
Where are your emails delivered?
Receive reports with an in-depth understanding of what your emails are doing and how to increase your reputation and deliverability before you hit Send!
In your reports you can:
❖ Check to see if your sending IPs or Domains are listed within 50+ major email blacklists.
❖ Protect your identity by identifying, monitoring, and rejecting unauthenticated outgoing emails.
❖ Identify whether your email’s content or reputation is being flagged as Spam by all major B2B and B2C email marketing providers.
❖ Fix HTML errors and identify “risky” content before sending.
❖ Get instantly notified when issues occur by email, Slack, or Telegram.
Want to speak with an expert?
Book a 1-hour consulting call to get all your email marketing and deliverability questions answered. We also offer comprehensive Email Deliverability Audits with personalized recommendations for companies looking to maximize their revenue with email.
Learn more about GlockApps
Debug Mail
How Debug Mail work
The service provides command-line access to the virtual SMTP-server. The sender and receiver addresses can be anything, since no real mailings are sent.
The technology used by application developers does not matter, the service will work with PHP, Python, Ruby, Node.js, .NET and many other programming languages and frameworks.
Sharing options
Sharing is the main feature of Debug Mail. To see what the service and other mailings will look like, just connect the right users to the project in the service, and they will see the same thing as the developer who is testing the mailing.
What you can do in Debug Mail
- Send emails to non-existent test addresses instead of real ones.
- Set up email distribution lists with colleagues using team access.
- Work together with other developers on the service.
Learn more about Debug Mail
Stripo.email
Stripo is an all-in-one email builder with over 1,700,000 users worldwide. We enable our clients to build emails of any complexity really fast — cutting production time by at least 3.7× — and push them to their marketing automation system with just one click. Integrated with 90+ ESPs/CRMs, including Mailchimp, HubSpot, Salesforce, Campaign Monitor, Constant Contact, Braze, SendGrid, eSputnik, Outlook, Gmail, etc.
1,700+ ready-to-use templates, modular email design, Email Translate Service, and built-in AI covering the full creative cycle — from campaign creation to copy, subject lines, images, and interactive widgets. A number of embedded micro-tools give you everything you need for emails, from photo editors to banner generators, from timers to interactivity and real-time content.
We are one of the first builders to implement the AMP4Email technology. Multiple studies show that AMP increases conversion by 5 times. With Stripo, you can build real-time content for your emails with
Learn more about Stripo.email
Pricing
Starting Price:
$49 per month
Free Version:
Free Version available.
Integrations
Company Information
Beyond Code
Founded: 2017
Germany
usehelo.com
Videos and Screen Captures
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Product Details
Platforms Supported
Mac
Training
Documentation
Live Online
Videos
Support
Online
HELO Frequently Asked Questions
Q: What kinds of users and organization types does HELO work with?
HELO works with these users and organization types: Mid Size Business, Small Business, Enterprise, Freelance, Nonprofit, Government, and Startup.
Q: What languages does HELO support in their product?
HELO supports these languages: English.
Q: What kind of support options does HELO offer?
HELO offers support via online.
Q: What other applications or services does HELO integrate with?
HELO integrates with: HTML.
Q: What type of training does HELO provide?
HELO provides training in the form of documentation, live online, and videos.
Q: How much does HELO cost?
Pricing for HELO starts at $49 per month.
