[Bug]: After import of cal.ics e-mail invite for a new attendee isn't sent

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• Nextcloud Server is running on 64bit capable CPU, PHP and OS.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

I'm using WordPress and Amelia for bookings. Amelia sends an email with an attachment named cal.ics

I can't upload the ics-files to this report but maybe it's needed. So this is the content of the file:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:https://hette-hette.de/wp-content/plugins/ameliabooking/
X-PUBLISHED-TTL:P1W
BEGIN:VEVENT
UID:64467a5069c71
DTSTART:20230503T071500Z
SEQUENCE:0
TRANSP:OPAQUE
DTEND:20230503T074500Z
LOCATION:online
SUMMARY:Onboarding Fortis
CLASS:PUBLIC
ORGANIZER;CN=Vincent Rammelt:MAILTO:vincent@projekt-r.hamburg
DTSTAMP:20230424T124712Z
END:VEVENT
END:VCALENDAR

If I import this file to my calendar, this step works.

If I want to add another invited person, the email wasn't sent (my own email address hosting service testmail@projekt-r.hamburg and even my private @gmail.com account are getting an invitation.

If I create a new appointment directly to my calendar and invite the same address, I'm getting the mail with that appointment.

Steps to reproduce

1. import cal.ics
2. enter email address
3. send invite

Expected behavior

Receiving an email.

Installation method

Community Web installer on a VPS or web space

Nextcloud Server version

26

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.1

Web server

Apache (supported)

Database engine version

MySQL

Is this bug present after an update or on a fresh install?

Updated from a minor version (ex. 22.2.3 to 22.2.4)

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

Server configuration detail

Operating system: Linux 5.10.0-20-amd64 nextcloud/server#1 SMP Debian 5.10.158-2 (2022-12-13) x86_64

Webserver: Apache (fpm-fcgi)

Database: mysql 10.5.18

PHP version: 8.1.13

Modules loaded: Core, date, libxml, openssl, pcre, zlib, filter, hash, json, Reflection, SPL, session, standard, sodium, cgi-fcgi, mysqlnd, PDO, xml, apcu, bcmath, bz2, calendar, ctype, curl, dom, mbstring, FFI, fileinfo, ftp, gd, gettext, gmp, iconv, igbinary, imagick, imap, intl, ldap, exif, mysqli, pdo_mysql, pdo_sqlite, Phar, posix, pspell, readline, shmop, SimpleXML, smbclient, soap, sockets, sqlite3, ssh2, sysvmsg, sysvsem, sysvshm, tidy, tokenizer, xmlreader, xmlrpc, xmlwriter, xsl, zip, libsmbclient, ionCube Loader, Zend OPcache

Nextcloud version: 26.0.1 - 26.0.1.1

Updated from an older Nextcloud/ownCloud or fresh install:

Where did you install Nextcloud from: unknown

List of activated Apps

Enabled:
 - activity: 2.18.0
 - announcementcenter: 6.5.1
 - bruteforcesettings: 2.6.0
 - calendar: 4.3.3
 - circles: 26.0.0
 - cloud_federation_api: 1.9.0
 - comments: 1.16.0
 - contacts: 5.2.0
 - contactsinteraction: 1.7.0
 - dashboard: 7.6.0
 - dav: 1.25.0
 - federatedfilesharing: 1.16.0
 - federation: 1.16.0
 - files: 1.21.1
 - files_pdfviewer: 2.7.0
 - files_rightclick: 1.5.0
 - files_sharing: 1.18.0
 - files_trashbin: 1.16.0
 - files_versions: 1.19.1
 - firstrunwizard: 2.15.0
 - google_synchronization: 1.0.9
 - groupfolders: 14.0.1
 - logreader: 2.11.0
 - lookup_server_connector: 1.14.0
 - mail: 3.1.1
 - nextcloud_announcements: 1.15.0
 - notifications: 2.14.0
 - oauth2: 1.14.0
 - password_policy: 1.16.0
 - photos: 2.2.0
 - privacy: 1.10.0
 - provisioning_api: 1.16.0
 - recommendations: 1.5.0
 - related_resources: 1.1.0-alpha1
 - serverinfo: 1.16.0
 - settings: 1.8.0
 - sharebymail: 1.16.0
 - spreed: 16.0.3
 - support: 1.9.0
 - survey_client: 1.14.0
 - systemtags: 1.16.0
 - text: 3.7.2
 - theming: 2.1.1
 - twofactor_backupcodes: 1.15.0
 - updatenotification: 1.16.0
 - user_status: 1.6.0
 - viewer: 1.10.0
 - weather_status: 1.6.0
 - workflowengine: 2.8.0
Disabled:
 - admin_audit
 - encryption
 - files_external
 - integration_jira: 1.0.4
 - mail_roundcube: 1.0.2
 - suspicious_login
 - twofactor_totp
 - user_ldap

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

No error in the logs

Additional info

No response

Start by reproducing the import-and-invite sequence with the supplied cal.ics content in the Nextcloud Calendar app, then trace the calendar import and attendee invitation flow. Compare it with an event created directly in the calendar; done means a newly added attendee receives the invitation email.