mail_failed when files attached larger than 2mb

Hi,

We have been using CF7 on a website for years, we have 2 fields in the contact form to allow a user to attach 2 photos to the form. This has always worked.

However we have noticed recently if the photo uploaded is greater than approx 2mb the form will not submit and just displays the “There was an error trying to send your message. Please try again later.” error, if we try to upload lower than this the form is sent successfully.

The fields in question have their max file size setting at 12mb, I have also checked over all the upload based PHP configuration values and these seem fine.

When the form is attempted to be sent I have checked in Dev Tools, and can see there is a ‘feedback’ request in the network tab when the form is submitted, after the spinner finishes and the error message appears we see this response in Dev Tools:

{"contact_form_id":123,"status":"mail_failed","message":"There was an error trying to send your message. Please try again later.","posted_data_hash":"e65c9a5e24384768f2566941a40ca9c1","into":"#wpcf7-f645-p21-o1","invalid_fields":[]}

Any help on why these larger images will not allow the form to be submitted? e.g. a 2mb will and a 3mb will not.