Error when change admin email from general settings

Warning: fopen(): Filename cannot be empty in /var/www/html/wp-content/plugins/mailgun/includes/wp-mail-api.php on line 265

Warning: fwrite() expects parameter 1 to be resource, boolean given in /var/www/html/wp-content/plugins/mailgun/includes/wp-mail-api.php on line 267

Warning: fclose() expects parameter 1 to be resource, boolean given in /var/www/html/wp-content/plugins/mailgun/includes/wp-mail-api.php on line 268

Warning: mime_content_type(): Can only process string or stream arguments in /var/www/html/wp-content/plugins/mailgun/includes/mg-filter.php on line 35

Warning: unlink(): No such file or directory in /var/www/html/wp-content/plugins/mailgun/includes/wp-mail-api.php on line 274

Warning: Cannot modify header information – headers already sent by (output started at /var/www/html/wp-content/plugins/mailgun/includes/wp-mail-api.php:265) in /var/www/html/wp-includes/pluggable.php on line 1216

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