E-mail sending twice

Hello.

Our team is developing a custom plugin that will send out a link to our post to a list e-mails upon being posted. The plugin is working properly, and after configuring the SMTP we got it to send the emails after posting.

The issue is that the e-mail logs confirm that our server is sending two e-mails at a time. We have added a error_log right after the wp_mail function and this confirms that the function is being called just once.

We tried the mail function, but no e-mails go out with that one.

We have even copied the source code for wp_mail and added an error_log upon sending, which again confirms that it is running the code just once, but somehow the e-mails go out two times.

What could we do to get to the core of this issue? We are aware that this could also be an SMTP / Server problem, but not sure how to proceed if so.

Our system info:

== Server Environment ==
	Operating System: Linux
	Software: Apache
	MySQL version: MySQL Community Server (GPL) v5.7.44
	PHP Version: 8.3.9
	PHP Memory Limit: 512M
	PHP Max Input Vars: 1000
	PHP Max Post Size: 8M
	GD Installed: Yes
	ZIP Installed: Yes
	Write Permissions: All right
	Elementor Library: Connected

== WordPress Environment ==
	Version: 6.6.1
	Site URL: https://paroquiadealjustrel.pt
	Home URL: https://paroquiadealjustrel.pt
	WP Multisite: No
	Max Upload Size: 8 MB
	Memory limit: 40M
	Max Memory limit: 512M
	Permalink Structure: /%postname%/
	Language: pt_PT
	Timezone: 0
	Admin Email: [email protected]
	Debug Mode: Inactive

== Theme ==
	Name: Hello Elementor
	Version: 3.1.0
	Author: Elementor Team
	Child Theme: No

== User ==
	Role: administrator
	WP Profile lang: pt-PT
	User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/127.0.0.0 Safari/537.36

== Active Plugins ==
	Check & Log Email
		Version: 1.0.13.1
		Author: checkemail

	Custom Post Notifier
		Version: 1.1
		Author: Your Name

	Disable Theme and Plugin Auto-Update Emails
		Version: 2.0.5
		Author: KZeni

	Elementor
		Version: 3.23.1
		Author: Elementor.com

	Elementor Header & Footer Builder
		Version: 1.6.37
		Author: Brainstorm Force, Nikhil Chavan

	Elementor Pro
		Version: 3.23.0
		Author: Elementor.com

	ElementsKit Lite
		Version: 3.2.1
		Author: Wpmet

	Envato Elements
		Version: 2.0.13
		Author: Envato

	Image Optimizer by Elementor – Compress, Resize and Optimize Images
		Version: 1.4.1
		Author: Elementor.com

	Jeg Elementor Kit
		Version: 2.6.7
		Author: Jegtheme

	Jetpack
		Version: 13.6
		Author: Automattic

	Jetpack Social
		Version: 4.5.2
		Author: Automattic - Jetpack Social team

	ManageWP - Worker
		Version: 4.9.20
		Author: GoDaddy

	MetForm
		Version: 3.8.9
		Author: Wpmet

	Política de Privacidade Automática
		Version: 1.0
		Author: Rodrigo Neves

	Revive Social
		Version: 9.1.0
		Author: revive.social

	Template Kit Import
		Version: 1.0.15
		Author: Envato

	WP Mail SMTP
		Version: 4.1.0
		Author: WP Mail SMTP

	Yoast Duplicate Post
		Version: 4.5
		Author: Enrico Battocchi & Team Yoast

	Yoast SEO
		Version: 23.0
		Author: Team Yoast


== Must-Use Plugins ==
	ManageWP - Worker Loader
		Version: 1.0.0
		Author: GoDaddy


== Elements Usage ==
	
	footer : 3
		copyright : 1
		divider : 1
		heading : 2
		icon-list : 2
		image : 1
		social-icons : 1
		text-editor : 1
	wp-page : 162
		button : 3
		container : 206
		divider : 1
		form : 1
		google_maps : 1
		heading : 98
		image : 55
		image-box : 5
		loop-grid : 1
		spacer : 97
		text-editor : 104
	single-post : 1
		container : 2
		heading : 1
		spacer : 1
		theme-post-content : 1
	loop-item : 2
		container : 3
		heading : 1
		theme-post-excerpt : 1
		theme-post-featured-image : 1
		theme-post-title : 1

Thank you,

Rodsn

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