I am using Apex to send emails with attachments to users (with SingleEmailMessage to be more precisely).

From some MB (I Don't sure exactly the size - because it changed from time to time when I try to check it) It converts the attaches files to .html files for downloading and store them in some CDN for a temporary time I guess.

I searched in Google but I confused between outbound and inbound and the email servers.

Can anyone please share with me the doc or have an answer for the size that I can send an outbound email from apex including attachments before it's converted to Html Links?

A little search in Google shows that people wrote that it limited for 3 - 5mb before it converts the attached file to .html links - But I tried it with 17 MB and it worked. (22 MB was converted to Html files).

Many thanks!

1 Answer 1


There is a setting that controls this limit. You'll find it in Setup under Email Attachments (use Quick Find to locate the setting). You can choose from either Always links, Emails over 3 MB, or Emails over maximum attachment limit. You can read more about this setting in KB 000249868.

  • Thanks @sfdcfox - But Where can I find the maximum attachment limit? 3 MB is very low to email with attachments... I succeed to send email attachments with a total size of 17 MB (one of the files was 15 MB alone). How can I know what is the maximum size?
    – Salvation
    Dec 19, 2018 at 7:39
  • @Salvation The maximum size should be 25 MB.
    – sfdcfox
    Dec 19, 2018 at 10:36

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