I'm trying to create a consistent underlined superscript across the client but it seems like bottom line always missaligned for some clients.

Superscript

Only solution close to what I'm trying to accomplish is #7 but still it's missaligned on some clients.

Here are the test results:
https://litmus.com/pub/765ff43

Here is the code:

            <tr>
                <td align="center" valign="top" style="text-decoration:underline;font-family:Arial, sans-serif; font-size:18px; line-height:18px; color:#000000;padding-bottom:20px;padding-top:20px;">
                    1. Underlined<sup>superscript</sup> test.
                </td>

            </tr>
            <tr>
                <td align="center" valign="top" style="text-decoration:underline;font-family:Arial, sans-serif; font-size:18px; line-height:18px; color:#000000;;padding-bottom:20px">
                    2. Underlined<sup style="font-size:11px; line-height:0px; vertical-align:7px; ">superscript</sup> test.
                </td>

            </tr>

            <tr>
                <td align="center" valign="top" style="text-decoration:underline;font-family:Arial, sans-serif; font-size:18px; line-height:18px; color:#000000;;padding-bottom:20px">
                    3. Underlined<sup style="line-height: 0; font-size: 60%;">superscript</sup> test.
                </td>
            </tr>

            <tr>
                <td align="center" valign="top" style="text-decoration:underline;font-family:Arial, sans-serif; font-size:18px; line-height:18px; color:#000000;;padding-bottom:20px">
                    4. Underlined<sup style="line-height: 0; font-size: 60%;">superscript</sup> test.
                </td>
            </tr>

            <tr>
                <td align="center" valign="top" style="text-decoration:underline;font-family:Arial, sans-serif; font-size:18px; line-height:18px; color:#000000;;padding-bottom:20px">
                    5. Underlined<sup style="font-size:60%;line-height:1;vertical-align:top;mso-text-raise: 30%;">superscript</sup> test.
                </td>
            </tr>
            <tr>
                <td align="center" valign="top" style="text-decoration:underline;font-family:Arial, sans-serif; font-size:18px; line-height:18px; color:#000000;;padding-bottom:20px">
                    6. Underlined<sup style="vertical-align: baseline;position: relative;top: -0.7em;font-size:0.5em;">superscript</sup> test.
                </td>
            </tr>
            <tr>
                <td align="center" valign="top" style="text-decoration:underline;font-family:Arial, sans-serif; font-size:18px; line-height:18px; color:#000000;;padding-bottom:20px">
                    7. Underlined<sup style="border-bottom-color: #000000;border-bottom-style: solid;border-width: 0 0 1px;display: inline-block;font-size: .60em;line-height: 1px;padding-bottom: 11px;">superscript</sup> test.
                </td>
            </tr>