Support » Plugin: MailPoet - emails and newsletters in WordPress » upgrade to MP 3 fails

  • I’m trying to upgrade from 2.8.1 to 3, but I’m getting this error consistently:

    Installatie mislukt (=install failed): <!DOCTYPE HTML PUBLIC “-//IETF//DTD HTML 2.0//EN”> 500 Internal Server Error Internal Server Error The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the server administrator, and inform them of the time the error occurred, and anything you might have done that may have caused the error. More information about this error may be available in the server error log.

    No problems with installing/updating other plugins. I don’t know where this “” is coming from. Our site is hosted at and in MailPoet 2 we are using to send newsletters.

    • This topic was modified 1 year, 9 months ago by willemb2.

    The page I need help with: [log in to see the link]

Viewing 6 replies - 1 through 6 (of 6 total)
  • Bruna


    Plugin Author MailPoet



    Try enabling the WordPress Debug mode to see if there’s a better error message than that one.

    This way, we’ll be able to find out what’s causing this.


    Have you checked the Minimum and Recommended Requirements for MailPoet 3?

    1. I have WordPress 4.9.2
    2. I have lots of images in my media gallery, so I assume the uploads folder is writable.
    3. PHP Version is 7.1.13
    4 and 5 are beyond my knowledge level. WordPress is pre-installed by our hosting provider STRATO. I do not have access on that level. All I can say is that MailPoet 2 and all other plugins work fine.


    I have looked all over our WordPress Dashboard, but I cannot find a setting to “enable Debug Mode”. In our case WordPress came pre-installed by the web-hosting provider. I found a plugin called Debug Mode, but that also fails to install, in this case without any error message.

    In the meantime we got MailPoet 3 running on a test website at another provider. We immediately ran into the problem described here. The workaround given there looks awful in our newsletters. We will not use MailPoet 3 until this is fixed. I really don’t understand the “upgrade to 3” nagging while such an essential feature of MailPoet 2 is still missing in MailPoet 3.

    I’m one step further, I think: someone advised me to disable all other plugins while installing MailPoet 3. After doing that, I still got the 500 Internal Server Error, but now MailPoet 3 does appear in the installed plugins list. However, I cannot activate it. The error message (in Dutch) says “could not connect to the database” and contains a link to this page.
    Solution 1 does not work. In our case DB_HOST =, if I change that to the whole site goes down with a “could not connect to the database” error.
    For I Solution 2 you need access to php.ini, but I do not have that. As I wrote above, this is a pre-installed WordPress. MailPoet 2 runs without (databes-) errors.

    STRATO support checked Solution 2, but the database connection is setup correctly. From phpinfo:
    PDO Driver for MySQL enabled
    Client API version 5.5.52
    Directive Local Value Master Value
    pdo_mysql.default_socket /tmp/mysql.sock /tmp/mysql.sock

    Here’s another thread with 6 people having the same problem:
    Unfortunately it has been closed and marked as solved by @mailpoet without publishing the solution that has been exchanged by e-mail with the OP 🙁

Viewing 6 replies - 1 through 6 (of 6 total)
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