Gmail Request Entity Too Large Error 413

First I would like to thank you for your great plugin.

I’m trying to create a form with “Contact Form 7” plugin that sends an email with uploaded files as attachments.

I receive the following error on WordPress admin panel when the attachment is larger than 5 mb. I can send attachments slightly smaller than that. This error also happens when I try to send, for example, 2 attachments each 3 mb.

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EMAIL DELIVERY ERROR: WP Mail SMTP plugin logged this error during the last time it tried to send an email:

Mailer: Gmail

Request Entity Too Large

Request Entity Too Large
Error 413

Please review your WP Mail SMTP settings in plugin admin area. Consider running an email test after fixing it.

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I tried to change the file size limit in .htaccess by adding:

php_value upload_max_filesize 128M
php_value post_max_size 128M
php_value max_execution_time 600
php_value max_input_time 600

in addition to php.ini by adding:

memory_limit = 128M
upload_max_filesize = 128M
post_max_size = 128M

in addition to my theme’s functions.php by adding:

@ini_set( ‘upload_max_size’ , ‘128M’ );
@ini_set( ‘post_max_size’, ‘128M’);
@ini_set( ‘max_execution_time’, ‘300’ );

I’m running WordPress 4.9.7, WP Mail SMTP 1.3.3, Contact Form 7 5.0.3 on a Debian GNU/Linux 9 (stretch) VPS.

I have followed https://wpforms.com/how-to-securely-send-wordpress-emails-using-gmail-smtp/ to configure WP Mail SMTP.

1. I can use the form to upload and email files as attachments up to 5 mib
2. When I try to choose a file larger than 5 mib:
2a. I see this error on “Contact Form 7”: “One or more fields have an error. Please check and try again.”
2b. I see WP Mail SMTP plugin error mentioned above on WordPress admin panel.
2c. I can confirm that files larger than 5mb are uploaded to the server using “Contact Form CFDB7”.

I am using Google’s G Suite and I can send larger attachments using the web browser.

I’m stuck right now, I would really appreciate any hint, thanks.