OFT vs. HTML Emails: Key Differences Developers Need to Know

Microsoft Outlook is one of the most widely used email clients in the world — with approximately 400 million users using it daily. Yet, many marketers have a love-hate relationship with the platform because of its complex rendering rules.

The fact is you can’t ignore the numbers. Instead, you have to make them work to your advantage. And that’s why we’re here to talk about Microsoft’s Outlook File Template (OFT). This specific format offers a low-cost alternative to campaign management software that’s quite different from the HTML development process most of us are used to, allowing teams to send branded, personalized email campaigns with ease.

At Assemble, we’ve spent countless hours researching, testing, and understanding how campaigns render differently across various clients, so that we can address any potential issues before they ever get to an inbox. Outlook is no different. So now, we’re sharing all the advantages and limitations of OFT emails when it comes to development.

What is Outlook File Template (OFT)?

OFT emails are a type of predesign email that allows messages to be sent with static or regular information. Essentially, it can be used as a foundation to start any new Outlook email.

For businesses, this template provides a simpler way to send emails that follow specific organization guidelines. Let’s say a company requires all employee emails to be branded with company colors, feature their logo, and utilize certain approved imagery. But depending on the sender, that company also wants it to be easily customizable so the sender can input their name, contact info, recipient info, file attachments, etc. to reach each of their unique databases. This is where OFT truly shines.

It’s also the only way to ensure your email campaigns will display properly on Outlook. Many features within a traditional HTML email (font style, images, background colors, etc.) won’t render properly on the Outlook platform. So to ensure your campaigns look exactly as they should, understanding how to develop for OFT is crucial.

OFT vs. Regular HTML Emails: Key Development Differences

  • Format: OFT is a proprietary format used by Microsoft Outlook; it’s not based on standard HTML like regular email development. OFT files are essentially an encapsulation of HTML, CSS, and other Outlook-specific components. Because of this, an HTML design is typically involved in the initial development of the template but requires multiple adjustments and considerations to meet Outlook’s OFT requirements.

  • CSS Support: OFT offers limited support for CSS styles compared to regular HTML, so many CSS properties that work in standard web browsers are not fully supported in Outlook, making email styling more challenging. An example is mobile responsiveness. In its creation, OFT deletes mobile styling that allows for this adaptation, so the campaign will show up the same on desktop as it does on a mobile device. For that reason, make sure text sizes and styling is large enough and easy to read.

  • Conditional Formatting: Unlike HTML, OFT allows for conditional formatting, so you can utilize specific styles for different versions of Outlook. In other words, if a certain element is compatible with Outlook but breaking on another client, developers can choose to hide that element when being received by that specific client — and still show up for Outlook.

OFT vs. Regular HTML Emails: Key Rendering Differences

  • CSS Support: Outlook has its own rendering engine, which varies from version to version. While newer versions may use a more modern rendering engine, there could still be inconsistencies in how CSS properties are interpreted. Outlook 2007, 2010, and 2013, all use Word, offering limited CSS support.

  • Assemble Pro Tip: Go as simple as possible with your design. Avoid web fonts, gradients, drop shadows, curves, overlays, GIFS, etc. that make the development much more difficult as it transfers to OFT. We love a pretty email as much as the next person, but you’ll only put your campaigns at higher risk of breaking across other clients. Keep CTAs clear and text-based to avoid issues and rely on your copy to do most of the heavy lifting.

  • Font Rendering: If you do use a web font, Outlook will often substitute it with a system font, which leads to differences in font rendering between Outlook and regular web browsers. Stick to Outlook’s safe for web font families (e.g., Arial) to avoid the system choosing your fonts for you.

  • Assemble Pro Tip: To avoid issues during customization, provide to the OFT template users with a set of guidelines to follow. Let them know which fields they specifically should modify and which they should leave as is. By making sure everyone is on the same page, you can rest assured all your company emails are delivered with quality and consistency.

  • Table-Based Layouts: Outlook is a lot more forgiving when it comes to table-based layouts, so developers often rely on this approach to achieve consistent rendering across Outlook clients.

  • Assemble Pro Tip: Keep your layout structure to just one column versus 2-3, so it displays correctly on multiple devices, including phones.

How Assemble Can Help

There are several specific limitations and rendering differences when using OFT to develop emails for Outlook — and it can be overwhelming. But when developed properly, it can be a highly effective, simplified, and cost-effective way for your teams to send out campaigns.

At Assemble, we know that the more we know about these nuances, the better we can help our clients create and deliver successful campaigns that meet all their unique goals. We know how to prioritize OFT conversion and address Outlook-specific issues within the template before tackling all the advancements you’re looking for. We also know that our clients don’t only use Outlook on Windows — they’re using Mac iOS as well. And that’s why Assemble delivers the OFT format on both the Windows PC system and an EMLTPL format which works the same way in Outlook for MAC.

Our email experts will help guide you through the design phase, offering recommendations that will ensure your emails will show up flawlessly across the necessary clients. To learn more, contact Assemble today.