However, there is a list of common “anti-spam” rules, and the size-related points are at the top of it. You won’t find strict and ubiquitous criteria for spam detection. Taking care to create a message that will be successfully delivered to your recipients, you should also think of which folder it will go to, how quickly it will be delivered, and how happy your recipients will be.Īvoiding spam filters and targeting the main folder of your recipient’s inbox is one of the trickiest things in email handling. What else should you consider about the size of your email? Moreover, some ESPs like Postmark have additional limits for the email body size. Spam score and rendering issues are the most important. However, besides general deliverability, there are few more concerns related to sending large messages. But it is still possible when you send numerous booking or order confirmations, for example. It’s a pretty rare situation when you need to send a mass email with large attachments. You can see that most email clients are capable of retrieving 20 – 25 MB of email data. TextBody and HtmlBody can each be up to 5 MB each Email clientĢ0 MB (10 MB for Exchange accounts), with up to 150 MB in Office 365 Limits for popular email sending providers and clients like Gmail, Outlook, Sendgrid, etc. If you work with a big database of email addresses to send transactional or marketing emails and don’t have such details about your recipients, you should follow a general rule: send messages that don’t exceed 10 MB. It is useful to know the allowance for your recipient’s incoming messages. limit to retrieve a message (your recipients’ mail system).įor example, if your email service is able to send messages up to 15 MB but the email recipient can retrieve messages only up to 10 MB, it’s obvious that your email should not exceed 10MB.limit to send a message (your email system).When preparing either transactional or marketing emails, you should consider two limits: This makes them candidates for DoS (denial of service) attacks: a huge amount of large messages can take the whole system down.
Email systems usually use a limited number of ports to retrieve data. Points 1 and 2 on our list also lead to potential security vulnerabilities. This is why not only the message itself but also the inbox as a whole has its own limits. Email data should be stored on a server (either cloud or local). In addition, mail transfer agents often scan incoming data for viruses and other potential risks, which also takes resources and affects system performance. Most of the systems are not able to process multiple data sources at once. They deal with SMTP, which is a quite outdated protocol. Email systems are not designed to transfer large volumes of data.
Also, there are some not so obvious factors, which impact the actual email size and deliverability. There are many things you should keep in mind when preparing your email notifications or newsletters: from the maximum size of file attachments and HTML part to the email client your recipients will most likely use. However, there is no unique standard – limits are dictated mostly by performance and security reasons. Every email sending provider has its own maximum email size limit.