Add the following code to your template from registeraddress: Resources/Private/Partial/Address/formFields.html
<div class="fieldrow form-group">
<f:alias map="{categories: '{od:getCategories()}'}">
<f:if condition="{categories}">
<f:if condition="{categories -> f:count()} == 1">
<f:then>
<f:comment>
We can't use the property attribute as we need the parameter to be
multiple (ending with []) in every case. This is not possible with the normal
hidden field. That's why we set the name by ourselves.
</f:comment>
<f:form.hidden name="newAddress[moduleSysDmailCategory][]" value="{categories.0.uid}" />
</f:then>
<f:else>
<fieldset class="checkboxes">
<f:for each="{categories}" as="category">
<f:form.checkbox
checked="{od:isCategorySelected(categoryUid: '{category.uid}')}"
id="option-{category.uid}"
class="category"
property="moduleSysDmailCategory"
multiple="1"
value="{category.uid}"
/>
<label for="option-{category.uid}">{category.category}</label>
</f:for>
</fieldset>
</f:else>
</f:if>
</f:if>
</f:alias>
</div>