# Cannot send emails to contacts or campaign

**URL:** <https://forum.mautic.org/t/cannot-send-emails-to-contacts-or-campaign/36115>\
**Category:** Mautic 6 Install/Upgrade Support\
**Created:** [July 17, 2025, 3:43am UTC](https://forum.mautic.org/t/cannot-send-emails-to-contacts-or-campaign/36115 "2025-07-17T03:43:16Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![zoltan.mark](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/zoltan.mark/32/13365_2.png) [@zoltan.mark](https://forum.mautic.org/u/zoltan.mark)\
**Post date:** [July 17, 2025, 3:43am UTC](https://forum.mautic.org/t/cannot-send-emails-to-contacts-or-campaign/36115/1 "2025-07-17T03:43:16Z")

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We’re on Mautic 6.0.2  
We send emails via an SMTP relay. The test email is successfully sent via settings and the test email arrives in the test mailbox.

I have a test contact with the same email address. I go there, click the Send email button. From name and address default to the contact I’m sending the email to, so I change these to Mautic’s display name and email address. Draft a simple email then hit send. I get Internal Server error 500 message.

mautic.prod.log has this  
[2025-07-17T03:29:54.836309+00:00] mautic.CRITICAL: Uncaught PHP Exception TypeError: “Mautic\CoreBundle\Helper\InputHelper::minifyHTML(): Argument #1 ($html) must be of type string, null given, called in /var/www/html/app/bundles/EmailBundle/Helper/MailHelper.php on line 1224” at /var/www/html/app/bundles/CoreBundle/Helper/InputHelper.php line 506 {“exception”:“[object] (TypeError(code: 0): Mautic\CoreBundle\Helper\InputHelper::minifyHTML(): Argument #1 ($html) must be of type string, null given, called in /var/www/html/app/bundles/EmailBundle/Helper/MailHelper.php on line 1224 at /var/www/html/app/bundles/CoreBundle/Helper/InputHelper.php:506)”} {“hostname”:“mautic”,“pid”:6865}

I close the popup window of the 500 error message. Instead of using my handwritten content, I select an email template to use, then send the email. I get a different error message  
Failed to send to [email address]: Expected response code “250/251/252” but got code “550”, with message “550 5.7.1 Command rejected”.

This email address is the same that works fine when testing via System settings.  
prod-[date].php log file has the same error message. No further details.

I don’t have access to the logs of the SMTP relay.

I then tried the following. Create a segment that targets this same, one single contact. I then created a campaign that sends a transactional email. This step uses the same email template as above. This email is not sent either. All I get is a small red exclamation mark in the campaign.

As the results contradict, I’m not sure where to next. I’d appreciate some help.

Cheers,  
Zoltan

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<div class="post-metadata">

**Author:** ![mattewwade06](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/mattewwade06/32/14401_2.png) [@mattewwade06](https://forum.mautic.org/u/mattewwade06)\
**Post date:** [September 9, 2025, 10:30am UTC](https://forum.mautic.org/t/cannot-send-emails-to-contacts-or-campaign/36115/2 "2025-09-09T10:30:10Z")

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Thanks for sharing the error details! Since your SMTP test works but campaign emails still fail, it may be related to how Mautic handles cron jobs and pending sends. A similar case was discussed here: [https://forum.mautic.org/t/](https://forum.mautic.org/t/emails-sending-problem-not-sent-to-all-contacts/34267)[estate agents london](https://realestateagentslondon.co.uk)[/emails-sending-problem-not-sent-to-all-contacts/34267](https://forum.mautic.org/t/emails-sending-problem-not-sent-to-all-contacts/34267)